1 /*
  2     Copyright 2008-2023
  3         Matthias Ehmann,
  4         Michael Gerhaeuser,
  5         Carsten Miller,
  6         Bianca Valentin,
  7         Alfred Wassermann,
  8         Peter Wilfahrt
  9 
 10     This file is part of JSXGraph.
 11 
 12     JSXGraph is free software dual licensed under the GNU LGPL or MIT License.
 13 
 14     You can redistribute it and/or modify it under the terms of the
 15 
 16       * GNU Lesser General Public License as published by
 17         the Free Software Foundation, either version 3 of the License, or
 18         (at your option) any later version
 19       OR
 20       * MIT License: https://github.com/jsxgraph/jsxgraph/blob/master/LICENSE.MIT
 21 
 22     JSXGraph is distributed in the hope that it will be useful,
 23     but WITHOUT ANY WARRANTY; without even the implied warranty of
 24     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 25     GNU Lesser General Public License for more details.
 26 
 27     You should have received a copy of the GNU Lesser General Public License and
 28     the MIT License along with JSXGraph. If not, see <https://www.gnu.org/licenses/>
 29     and <https://opensource.org/licenses/MIT/>.
 30  */
 31 
 32 /*global JXG: true, define: true*/
 33 /*jslint nomen: true, plusplus: true*/
 34 
 35 /**
 36  * @fileoverview In this file the geometry element Curve is defined.
 37  */
 38 
 39 import JXG from "../jxg";
 40 import Clip from "../math/clip";
 41 import Const from "./constants";
 42 import Coords from "./coords";
 43 import Geometry from "../math/geometry";
 44 import GeometryElement from "./element";
 45 import GeonextParser from "../parser/geonext";
 46 import ImplicitPlot from "../math/implicitplot";
 47 import Mat from "../math/math";
 48 import Metapost from "../math/metapost";
 49 import Numerics from "../math/numerics";
 50 import Plot from "../math/plot";
 51 import QDT from "../math/qdt";
 52 import Type from "../utils/type";
 53 
 54 /**
 55  * Curves are the common object for function graphs, parametric curves, polar curves, and data plots.
 56  * @class Creates a new curve object. Do not use this constructor to create a curve. Use {@link JXG.Board#create} with
 57  * type {@link Curve}, or {@link Functiongraph} instead.
 58  * @augments JXG.GeometryElement
 59  * @param {String|JXG.Board} board The board the new curve is drawn on.
 60  * @param {Array} parents defining terms An array with the function terms or the data points of the curve.
 61  * @param {Object} attributes Defines the visual appearance of the curve.
 62  * @see JXG.Board#generateName
 63  * @see JXG.Board#addCurve
 64  */
 65 JXG.Curve = function (board, parents, attributes) {
 66     this.constructor(board, attributes, Const.OBJECT_TYPE_CURVE, Const.OBJECT_CLASS_CURVE);
 67 
 68     this.points = [];
 69     /**
 70      * Number of points on curves. This value changes
 71      * between numberPointsLow and numberPointsHigh.
 72      * It is set in {@link JXG.Curve#updateCurve}.
 73      */
 74     this.numberPoints = Type.evaluate(this.visProp.numberpointshigh);
 75 
 76     this.bezierDegree = 1;
 77 
 78     /**
 79      * Array holding the x-coordinates of a data plot.
 80      * This array can be updated during run time by overwriting
 81      * the method {@link JXG.Curve#updateDataArray}.
 82      * @type array
 83      */
 84     this.dataX = null;
 85 
 86     /**
 87      * Array holding the y-coordinates of a data plot.
 88      * This array can be updated during run time by overwriting
 89      * the method {@link JXG.Curve#updateDataArray}.
 90      * @type array
 91      */
 92     this.dataY = null;
 93 
 94     /**
 95      * Array of ticks storing all the ticks on this curve. Do not set this field directly and use
 96      * {@link JXG.Curve#addTicks} and {@link JXG.Curve#removeTicks} to add and remove ticks to and
 97      * from the curve.
 98      * @type Array
 99      * @see JXG.Ticks
100      */
101     this.ticks = [];
102 
103     /**
104      * Stores a quadtree if it is required. The quadtree is generated in the curve
105      * updates and can be used to speed up the hasPoint method.
106      * @type JXG.Math.Quadtree
107      */
108     this.qdt = null;
109 
110     if (Type.exists(parents[0])) {
111         this.varname = parents[0];
112     } else {
113         this.varname = "x";
114     }
115 
116     // function graphs: "x"
117     this.xterm = parents[1];
118     // function graphs: e.g. "x^2"
119     this.yterm = parents[2];
120 
121     // Converts GEONExT syntax into JavaScript syntax
122     this.generateTerm(this.varname, this.xterm, this.yterm, parents[3], parents[4]);
123     // First evaluation of the curve
124     this.updateCurve();
125 
126     this.id = this.board.setId(this, "G");
127     this.board.renderer.drawCurve(this);
128 
129     this.board.finalizeAdding(this);
130 
131     this.createGradient();
132     this.elType = "curve";
133     this.createLabel();
134 
135     if (Type.isString(this.xterm)) {
136         this.notifyParents(this.xterm);
137     }
138     if (Type.isString(this.yterm)) {
139         this.notifyParents(this.yterm);
140     }
141 
142     this.methodMap = Type.deepCopy(this.methodMap, {
143         generateTerm: "generateTerm",
144         setTerm: "generateTerm",
145         move: "moveTo",
146         moveTo: "moveTo",
147         MinX: "minX",
148         MaxX: "maxX"
149     });
150 };
151 
152 JXG.Curve.prototype = new GeometryElement();
153 
154 JXG.extend(
155     JXG.Curve.prototype,
156     /** @lends JXG.Curve.prototype */ {
157         /**
158          * Gives the default value of the left bound for the curve.
159          * May be overwritten in {@link JXG.Curve#generateTerm}.
160          * @returns {Number} Left bound for the curve.
161          */
162         minX: function () {
163             var leftCoords;
164 
165             if (Type.evaluate(this.visProp.curvetype) === "polar") {
166                 return 0;
167             }
168 
169             leftCoords = new Coords(
170                 Const.COORDS_BY_SCREEN,
171                 [-this.board.canvasWidth * 0.1, 0],
172                 this.board,
173                 false
174             );
175             return leftCoords.usrCoords[1];
176         },
177 
178         /**
179          * Gives the default value of the right bound for the curve.
180          * May be overwritten in {@link JXG.Curve#generateTerm}.
181          * @returns {Number} Right bound for the curve.
182          */
183         maxX: function () {
184             var rightCoords;
185 
186             if (Type.evaluate(this.visProp.curvetype) === "polar") {
187                 return 2 * Math.PI;
188             }
189             rightCoords = new Coords(
190                 Const.COORDS_BY_SCREEN,
191                 [this.board.canvasWidth * 1.1, 0],
192                 this.board,
193                 false
194             );
195 
196             return rightCoords.usrCoords[1];
197         },
198 
199         /**
200          * The parametric function which defines the x-coordinate of the curve.
201          * @param {Number} t A number between {@link JXG.Curve#minX} and {@link JXG.Curve#maxX}.
202          * @param {Boolean} suspendUpdate A boolean flag which is false for the
203          * first call of the function during a fresh plot of the curve and true
204          * for all subsequent calls of the function. This may be used to speed up the
205          * plotting of the curve, if the e.g. the curve depends on some input elements.
206          * @returns {Number} x-coordinate of the curve at t.
207          */
208         X: function (t) {
209             return NaN;
210         },
211 
212         /**
213          * The parametric function which defines the y-coordinate of the curve.
214          * @param {Number} t A number between {@link JXG.Curve#minX} and {@link JXG.Curve#maxX}.
215          * @param {Boolean} suspendUpdate A boolean flag which is false for the
216          * first call of the function during a fresh plot of the curve and true
217          * for all subsequent calls of the function. This may be used to speed up the
218          * plotting of the curve, if the e.g. the curve depends on some input elements.
219          * @returns {Number} y-coordinate of the curve at t.
220          */
221         Y: function (t) {
222             return NaN;
223         },
224 
225         /**
226          * Treat the curve as curve with homogeneous coordinates.
227          * @param {Number} t A number between {@link JXG.Curve#minX} and {@link JXG.Curve#maxX}.
228          * @returns {Number} Always 1.0
229          */
230         Z: function (t) {
231             return 1;
232         },
233 
234         /**
235          * Checks whether (x,y) is near the curve.
236          * @param {Number} x Coordinate in x direction, screen coordinates.
237          * @param {Number} y Coordinate in y direction, screen coordinates.
238          * @param {Number} start Optional start index for search on data plots.
239          * @returns {Boolean} True if (x,y) is near the curve, False otherwise.
240          */
241         hasPoint: function (x, y, start) {
242             var t, c, i, tX, tY,
243                 checkPoint, len, invMat, isIn,
244                 res = [],
245                 points,
246                 qdt,
247                 steps = Type.evaluate(this.visProp.numberpointslow),
248                 d = (this.maxX() - this.minX()) / steps,
249                 prec, type,
250                 dist = Infinity,
251                 ux2, uy2,
252                 ev_ct,
253                 mi, ma,
254                 suspendUpdate = true;
255 
256             if (Type.isObject(Type.evaluate(this.visProp.precision))) {
257                 type = this.board._inputDevice;
258                 prec = Type.evaluate(this.visProp.precision[type]);
259             } else {
260                 // 'inherit'
261                 prec = this.board.options.precision.hasPoint;
262             }
263 
264             // From now on, x,y are usrCoords
265             checkPoint = new Coords(Const.COORDS_BY_SCREEN, [x, y], this.board, false);
266             x = checkPoint.usrCoords[1];
267             y = checkPoint.usrCoords[2];
268 
269             // Handle inner points of the curve
270             if (this.bezierDegree === 1 && Type.evaluate(this.visProp.hasinnerpoints)) {
271                 isIn = Geometry.windingNumber([1, x, y], this.points, true);
272                 if (isIn !== 0) {
273                     return true;
274                 }
275             }
276 
277             // We use usrCoords. Only in the final distance calculation
278             // screen coords are used
279             prec += Type.evaluate(this.visProp.strokewidth) * 0.5;
280             prec *= prec; // We do not want to take sqrt
281             ux2 = this.board.unitX * this.board.unitX;
282             uy2 = this.board.unitY * this.board.unitY;
283 
284             mi = this.minX();
285             ma = this.maxX();
286             if (Type.exists(this._visibleArea)) {
287                 mi = this._visibleArea[0];
288                 ma = this._visibleArea[1];
289                 d = (ma - mi) / steps;
290             }
291 
292             ev_ct = Type.evaluate(this.visProp.curvetype);
293             if (ev_ct === "parameter" || ev_ct === "polar") {
294                 // Transform the mouse/touch coordinates
295                 // back to the original position of the curve.
296                 // This is needed, because we work with the function terms, not the points.
297                 if (this.transformations.length > 0) {
298                     this.updateTransformMatrix();
299                     invMat = Mat.inverse(this.transformMat);
300                     c = Mat.matVecMult(invMat, [1, x, y]);
301                     x = c[1];
302                     y = c[2];
303                 }
304 
305                 // Brute force search for a point on the curve close to the mouse pointer
306                 for (i = 0, t = mi; i < steps; i++) {
307                     tX = this.X(t, suspendUpdate);
308                     tY = this.Y(t, suspendUpdate);
309 
310                     dist = (x - tX) * (x - tX) * ux2 + (y - tY) * (y - tY) * uy2;
311 
312                     if (dist <= prec) {
313                         return true;
314                     }
315 
316                     t += d;
317                 }
318             } else if (ev_ct === "plot" || ev_ct === "functiongraph") {
319                 // Here, we can ignore transformations of the curve,
320                 // since we are working directly with the points.
321 
322                 if (!Type.exists(start) || start < 0) {
323                     start = 0;
324                 }
325 
326                 if (
327                     Type.exists(this.qdt) &&
328                     Type.evaluate(this.visProp.useqdt) &&
329                     this.bezierDegree !== 3
330                 ) {
331                     qdt = this.qdt.query(new Coords(Const.COORDS_BY_USER, [x, y], this.board));
332                     points = qdt.points;
333                     len = points.length;
334                 } else {
335                     points = this.points;
336                     len = this.numberPoints - 1;
337                 }
338 
339                 for (i = start; i < len; i++) {
340                     if (this.bezierDegree === 3) {
341                         //res.push(Geometry.projectCoordsToBeziersegment([1, x, y], this, i));
342                         res = Geometry.projectCoordsToBeziersegment([1, x, y], this, i);
343                     } else {
344                         if (qdt) {
345                             if (points[i].prev) {
346                                 res = Geometry.projectCoordsToSegment(
347                                     [1, x, y],
348                                     points[i].prev.usrCoords,
349                                     points[i].usrCoords
350                                 );
351                             }
352 
353                             // If the next point in the array is the same as the current points
354                             // next neighbor we don't have to project it onto that segment because
355                             // that will already be done in the next iteration of this loop.
356                             if (points[i].next && points[i + 1] !== points[i].next) {
357                                 res = Geometry.projectCoordsToSegment(
358                                     [1, x, y],
359                                     points[i].usrCoords,
360                                     points[i].next.usrCoords
361                                 );
362                             }
363                         } else {
364                             res = Geometry.projectCoordsToSegment(
365                                 [1, x, y],
366                                 points[i].usrCoords,
367                                 points[i + 1].usrCoords
368                             );
369                         }
370                     }
371 
372                     if (
373                         res[1] >= 0 &&
374                         res[1] <= 1 &&
375                         (x - res[0][1]) * (x - res[0][1]) * ux2 +
376                             (y - res[0][2]) * (y - res[0][2]) * uy2 <=
377                             prec
378                     ) {
379                         return true;
380                     }
381                 }
382                 return false;
383             }
384             return dist < prec;
385         },
386 
387         /**
388          * Allocate points in the Coords array this.points
389          */
390         allocatePoints: function () {
391             var i, len;
392 
393             len = this.numberPoints;
394 
395             if (this.points.length < this.numberPoints) {
396                 for (i = this.points.length; i < len; i++) {
397                     this.points[i] = new Coords(
398                         Const.COORDS_BY_USER,
399                         [0, 0],
400                         this.board,
401                         false
402                     );
403                 }
404             }
405         },
406 
407         /**
408          * Computes for equidistant points on the x-axis the values of the function
409          * @returns {JXG.Curve} Reference to the curve object.
410          * @see JXG.Curve#updateCurve
411          */
412         update: function () {
413             if (this.needsUpdate) {
414                 if (Type.evaluate(this.visProp.trace)) {
415                     this.cloneToBackground(true);
416                 }
417                 this.updateCurve();
418             }
419 
420             return this;
421         },
422 
423         /**
424          * Updates the visual contents of the curve.
425          * @returns {JXG.Curve} Reference to the curve object.
426          */
427         updateRenderer: function () {
428             //var wasReal;
429 
430             if (!this.needsUpdate) {
431                 return this;
432             }
433 
434             if (this.visPropCalc.visible) {
435                 // wasReal = this.isReal;
436 
437                 this.isReal = Plot.checkReal(this.points);
438 
439                 if (
440                     //wasReal &&
441                     !this.isReal
442                 ) {
443                     this.updateVisibility(false);
444                 }
445             }
446 
447             if (this.visPropCalc.visible) {
448                 this.board.renderer.updateCurve(this);
449             }
450 
451             /* Update the label if visible. */
452             if (
453                 this.hasLabel &&
454                 this.visPropCalc.visible &&
455                 this.label &&
456                 this.label.visPropCalc.visible &&
457                 this.isReal
458             ) {
459                 this.label.update();
460                 this.board.renderer.updateText(this.label);
461             }
462 
463             // Update rendNode display
464             this.setDisplayRendNode();
465             // if (this.visPropCalc.visible !== this.visPropOld.visible) {
466             //     this.board.renderer.display(this, this.visPropCalc.visible);
467             //     this.visPropOld.visible = this.visPropCalc.visible;
468             //
469             //     if (this.hasLabel) {
470             //         this.board.renderer.display(this.label, this.label.visPropCalc.visible);
471             //     }
472             // }
473 
474             this.needsUpdate = false;
475             return this;
476         },
477 
478         /**
479          * For dynamic dataplots updateCurve can be used to compute new entries
480          * for the arrays {@link JXG.Curve#dataX} and {@link JXG.Curve#dataY}. It
481          * is used in {@link JXG.Curve#updateCurve}. Default is an empty method, can
482          * be overwritten by the user.
483          *
484          *
485          * @example
486          * // This example overwrites the updateDataArray method.
487          * // There, new values for the arrays JXG.Curve.dataX and JXG.Curve.dataY
488          * // are computed from the value of the slider N
489          *
490          * var N = board.create('slider', [[0,1.5],[3,1.5],[1,3,40]], {name:'n',snapWidth:1});
491          * var circ = board.create('circle',[[4,-1.5],1],{strokeWidth:1, strokecolor:'black', strokeWidth:2,
492          * 		fillColor:'#0055ff13'});
493          *
494          * var c = board.create('curve', [[0],[0]],{strokecolor:'red', strokeWidth:2});
495          * c.updateDataArray = function() {
496          *         var r = 1, n = Math.floor(N.Value()),
497          *             x = [0], y = [0],
498          *             phi = Math.PI/n,
499          *             h = r*Math.cos(phi),
500          *             s = r*Math.sin(phi),
501          *             i, j,
502          *             px = 0, py = 0, sgn = 1,
503          *             d = 16,
504          *             dt = phi/d,
505          *             pt;
506          *
507          *         for (i = 0; i < n; i++) {
508          *             for (j = -d; j <= d; j++) {
509          *                 pt = dt*j;
510          *                 x.push(px + r*Math.sin(pt));
511          *                 y.push(sgn*r*Math.cos(pt) - (sgn-1)*h*0.5);
512          *             }
513          *             px += s;
514          *             sgn *= (-1);
515          *         }
516          *         x.push((n - 1)*s);
517          *         y.push(h + (sgn - 1)*h*0.5);
518          *         this.dataX = x;
519          *         this.dataY = y;
520          *     }
521          *
522          * var c2 = board.create('curve', [[0],[0]],{strokecolor:'red', strokeWidth:1});
523          * c2.updateDataArray = function() {
524          *         var r = 1, n = Math.floor(N.Value()),
525          *             px = circ.midpoint.X(), py = circ.midpoint.Y(),
526          *             x = [px], y = [py],
527          *             phi = Math.PI/n,
528          *             s = r*Math.sin(phi),
529          *             i, j,
530          *             d = 16,
531          *             dt = phi/d,
532          *             pt = Math.PI*0.5+phi;
533          *
534          *         for (i = 0; i < n; i++) {
535          *             for (j= -d; j <= d; j++) {
536          *                 x.push(px + r*Math.cos(pt));
537          *                 y.push(py + r*Math.sin(pt));
538          *                 pt -= dt;
539          *             }
540          *             x.push(px);
541          *             y.push(py);
542          *             pt += dt;
543          *         }
544          *         this.dataX = x;
545          *         this.dataY = y;
546          *     }
547          *     board.update();
548          *
549          * </pre><div id="JXG20bc7802-e69e-11e5-b1bf-901b0e1b8723" class="jxgbox" style="width: 600px; height: 400px;"></div>
550          * <script type="text/javascript">
551          *     (function() {
552          *         var board = JXG.JSXGraph.initBoard('JXG20bc7802-e69e-11e5-b1bf-901b0e1b8723',
553          *             {boundingbox: [-1.5,2,8,-3], keepaspectratio: true, axis: true, showcopyright: false, shownavigation: false});
554          *             var N = board.create('slider', [[0,1.5],[3,1.5],[1,3,40]], {name:'n',snapWidth:1});
555          *             var circ = board.create('circle',[[4,-1.5],1],{strokeWidth:1, strokecolor:'black',
556          *             strokeWidth:2, fillColor:'#0055ff13'});
557          *
558          *             var c = board.create('curve', [[0],[0]],{strokecolor:'red', strokeWidth:2});
559          *             c.updateDataArray = function() {
560          *                     var r = 1, n = Math.floor(N.Value()),
561          *                         x = [0], y = [0],
562          *                         phi = Math.PI/n,
563          *                         h = r*Math.cos(phi),
564          *                         s = r*Math.sin(phi),
565          *                         i, j,
566          *                         px = 0, py = 0, sgn = 1,
567          *                         d = 16,
568          *                         dt = phi/d,
569          *                         pt;
570          *
571          *                     for (i=0;i<n;i++) {
572          *                         for (j=-d;j<=d;j++) {
573          *                             pt = dt*j;
574          *                             x.push(px+r*Math.sin(pt));
575          *                             y.push(sgn*r*Math.cos(pt)-(sgn-1)*h*0.5);
576          *                         }
577          *                         px += s;
578          *                         sgn *= (-1);
579          *                     }
580          *                     x.push((n-1)*s);
581          *                     y.push(h+(sgn-1)*h*0.5);
582          *                     this.dataX = x;
583          *                     this.dataY = y;
584          *                 }
585          *
586          *             var c2 = board.create('curve', [[0],[0]],{strokecolor:'red', strokeWidth:1});
587          *             c2.updateDataArray = function() {
588          *                     var r = 1, n = Math.floor(N.Value()),
589          *                         px = circ.midpoint.X(), py = circ.midpoint.Y(),
590          *                         x = [px], y = [py],
591          *                         phi = Math.PI/n,
592          *                         s = r*Math.sin(phi),
593          *                         i, j,
594          *                         d = 16,
595          *                         dt = phi/d,
596          *                         pt = Math.PI*0.5+phi;
597          *
598          *                     for (i=0;i<n;i++) {
599          *                         for (j=-d;j<=d;j++) {
600          *                             x.push(px+r*Math.cos(pt));
601          *                             y.push(py+r*Math.sin(pt));
602          *                             pt -= dt;
603          *                         }
604          *                         x.push(px);
605          *                         y.push(py);
606          *                         pt += dt;
607          *                     }
608          *                     this.dataX = x;
609          *                     this.dataY = y;
610          *                 }
611          *                 board.update();
612          *
613          *     })();
614          *
615          * </script><pre>
616          *
617          * @example
618          * // This is an example which overwrites updateDataArray and produces
619          * // a Bezier curve of degree three.
620          * var A = board.create('point', [-3,3]);
621          * var B = board.create('point', [3,-2]);
622          * var line = board.create('segment', [A,B]);
623          *
624          * var height = 0.5; // height of the curly brace
625          *
626          * // Curly brace
627          * var crl = board.create('curve', [[0],[0]], {strokeWidth:1, strokeColor:'black'});
628          * crl.bezierDegree = 3;
629          * crl.updateDataArray = function() {
630          *     var d = [B.X()-A.X(), B.Y()-A.Y()],
631          *         dl = Math.sqrt(d[0]*d[0]+d[1]*d[1]),
632          *         mid = [(A.X()+B.X())*0.5, (A.Y()+B.Y())*0.5];
633          *
634          *     d[0] *= height/dl;
635          *     d[1] *= height/dl;
636          *
637          *     this.dataX = [ A.X(), A.X()-d[1], mid[0], mid[0]-d[1], mid[0], B.X()-d[1], B.X() ];
638          *     this.dataY = [ A.Y(), A.Y()+d[0], mid[1], mid[1]+d[0], mid[1], B.Y()+d[0], B.Y() ];
639          * };
640          *
641          * // Text
642          * var txt = board.create('text', [
643          *                     function() {
644          *                         var d = [B.X()-A.X(), B.Y()-A.Y()],
645          *                             dl = Math.sqrt(d[0]*d[0]+d[1]*d[1]),
646          *                             mid = (A.X()+B.X())*0.5;
647          *
648          *                         d[1] *= height/dl;
649          *                         return mid-d[1]+0.1;
650          *                     },
651          *                     function() {
652          *                         var d = [B.X()-A.X(), B.Y()-A.Y()],
653          *                             dl = Math.sqrt(d[0]*d[0]+d[1]*d[1]),
654          *                             mid = (A.Y()+B.Y())*0.5;
655          *
656          *                         d[0] *= height/dl;
657          *                         return mid+d[0]+0.1;
658          *                     },
659          *                     function() { return "length=" + JXG.toFixed(B.Dist(A), 2); }
660          *                 ]);
661          *
662          *
663          * board.update(); // This update is necessary to call updateDataArray the first time.
664          *
665          * </pre><div id="JXGa61a4d66-e69f-11e5-b1bf-901b0e1b8723"  class="jxgbox" style="width: 300px; height: 300px;"></div>
666          * <script type="text/javascript">
667          *     (function() {
668          *      var board = JXG.JSXGraph.initBoard('JXGa61a4d66-e69f-11e5-b1bf-901b0e1b8723',
669          *             {boundingbox: [-4, 4, 4,-4], axis: true, showcopyright: false, shownavigation: false});
670          *     var A = board.create('point', [-3,3]);
671          *     var B = board.create('point', [3,-2]);
672          *     var line = board.create('segment', [A,B]);
673          *
674          *     var height = 0.5; // height of the curly brace
675          *
676          *     // Curly brace
677          *     var crl = board.create('curve', [[0],[0]], {strokeWidth:1, strokeColor:'black'});
678          *     crl.bezierDegree = 3;
679          *     crl.updateDataArray = function() {
680          *         var d = [B.X()-A.X(), B.Y()-A.Y()],
681          *             dl = Math.sqrt(d[0]*d[0]+d[1]*d[1]),
682          *             mid = [(A.X()+B.X())*0.5, (A.Y()+B.Y())*0.5];
683          *
684          *         d[0] *= height/dl;
685          *         d[1] *= height/dl;
686          *
687          *         this.dataX = [ A.X(), A.X()-d[1], mid[0], mid[0]-d[1], mid[0], B.X()-d[1], B.X() ];
688          *         this.dataY = [ A.Y(), A.Y()+d[0], mid[1], mid[1]+d[0], mid[1], B.Y()+d[0], B.Y() ];
689          *     };
690          *
691          *     // Text
692          *     var txt = board.create('text', [
693          *                         function() {
694          *                             var d = [B.X()-A.X(), B.Y()-A.Y()],
695          *                                 dl = Math.sqrt(d[0]*d[0]+d[1]*d[1]),
696          *                                 mid = (A.X()+B.X())*0.5;
697          *
698          *                             d[1] *= height/dl;
699          *                             return mid-d[1]+0.1;
700          *                         },
701          *                         function() {
702          *                             var d = [B.X()-A.X(), B.Y()-A.Y()],
703          *                                 dl = Math.sqrt(d[0]*d[0]+d[1]*d[1]),
704          *                                 mid = (A.Y()+B.Y())*0.5;
705          *
706          *                             d[0] *= height/dl;
707          *                             return mid+d[0]+0.1;
708          *                         },
709          *                         function() { return "length="+JXG.toFixed(B.Dist(A), 2); }
710          *                     ]);
711          *
712          *
713          *     board.update(); // This update is necessary to call updateDataArray the first time.
714          *
715          *     })();
716          *
717          * </script><pre>
718          *
719          *
720          */
721         updateDataArray: function () {
722             // this used to return this, but we shouldn't rely on the user to implement it.
723         },
724 
725         /**
726          * Computes the curve path
727          * @see JXG.Curve#update
728          * @returns {JXG.Curve} Reference to the curve object.
729          */
730         updateCurve: function () {
731             var i, len,  mi, ma,
732                 x, y,
733                 version = this.visProp.plotversion,
734                 //t1, t2, l1,
735                 suspendUpdate = false;
736 
737             this.updateTransformMatrix();
738             this.updateDataArray();
739             mi = this.minX();
740             ma = this.maxX();
741 
742             // Discrete data points
743             // x-coordinates are in an array
744             if (Type.exists(this.dataX)) {
745                 this.numberPoints = this.dataX.length;
746                 len = this.numberPoints;
747 
748                 // It is possible, that the array length has increased.
749                 this.allocatePoints();
750 
751                 for (i = 0; i < len; i++) {
752                     x = i;
753 
754                     // y-coordinates are in an array
755                     if (Type.exists(this.dataY)) {
756                         y = i;
757                         // The last parameter prevents rounding in usr2screen().
758                         this.points[i].setCoordinates(
759                             Const.COORDS_BY_USER,
760                             [this.dataX[i], this.dataY[i]],
761                             false
762                         );
763                     } else {
764                         // discrete x data, continuous y data
765                         y = this.X(x);
766                         // The last parameter prevents rounding in usr2screen().
767                         this.points[i].setCoordinates(
768                             Const.COORDS_BY_USER,
769                             [this.dataX[i], this.Y(y, suspendUpdate)],
770                             false
771                         );
772                     }
773                     this.points[i]._t = i;
774 
775                     // this.updateTransform(this.points[i]);
776                     suspendUpdate = true;
777                 }
778                 // continuous x data
779             } else {
780                 if (Type.evaluate(this.visProp.doadvancedplot)) {
781                     // console.time("plot");
782 
783                     if (version === 1 || Type.evaluate(this.visProp.doadvancedplotold)) {
784                         Plot.updateParametricCurveOld(this, mi, ma);
785                     } else if (version === 2) {
786                         Plot.updateParametricCurve_v2(this, mi, ma);
787                     } else if (version === 3) {
788                         Plot.updateParametricCurve_v3(this, mi, ma);
789                     } else if (version === 4) {
790                         Plot.updateParametricCurve_v4(this, mi, ma);
791                     } else {
792                         Plot.updateParametricCurve_v2(this, mi, ma);
793                     }
794                     // console.timeEnd("plot");
795                 } else {
796                     if (this.board.updateQuality === this.board.BOARD_QUALITY_HIGH) {
797                         this.numberPoints = Type.evaluate(this.visProp.numberpointshigh);
798                     } else {
799                         this.numberPoints = Type.evaluate(this.visProp.numberpointslow);
800                     }
801 
802                     // It is possible, that the array length has increased.
803                     this.allocatePoints();
804                     Plot.updateParametricCurveNaive(this, mi, ma, this.numberPoints);
805                 }
806                 len = this.numberPoints;
807 
808                 if (
809                     Type.evaluate(this.visProp.useqdt) &&
810                     this.board.updateQuality === this.board.BOARD_QUALITY_HIGH
811                 ) {
812                     this.qdt = new QDT(this.board.getBoundingBox());
813                     for (i = 0; i < this.points.length; i++) {
814                         this.qdt.insert(this.points[i]);
815 
816                         if (i > 0) {
817                             this.points[i].prev = this.points[i - 1];
818                         }
819 
820                         if (i < len - 1) {
821                             this.points[i].next = this.points[i + 1];
822                         }
823                     }
824                 }
825 
826                 // for (i = 0; i < len; i++) {
827                 //     this.updateTransform(this.points[i]);
828                 // }
829             }
830 
831             if (
832                 Type.evaluate(this.visProp.curvetype) !== "plot" &&
833                 Type.evaluate(this.visProp.rdpsmoothing)
834             ) {
835                 // console.time("rdp");
836                 this.points = Numerics.RamerDouglasPeucker(this.points, 0.2);
837                 this.numberPoints = this.points.length;
838                 // console.timeEnd("rdp");
839                 // console.log(this.numberPoints);
840             }
841 
842             len = this.numberPoints;
843             for (i = 0; i < len; i++) {
844                 this.updateTransform(this.points[i]);
845             }
846 
847             return this;
848         },
849 
850         updateTransformMatrix: function () {
851             var t,
852                 i,
853                 len = this.transformations.length;
854 
855             this.transformMat = [
856                 [1, 0, 0],
857                 [0, 1, 0],
858                 [0, 0, 1]
859             ];
860 
861             for (i = 0; i < len; i++) {
862                 t = this.transformations[i];
863                 t.update();
864                 this.transformMat = Mat.matMatMult(t.matrix, this.transformMat);
865             }
866 
867             return this;
868         },
869 
870         /**
871          * Applies the transformations of the curve to the given point <tt>p</tt>.
872          * Before using it, {@link JXG.Curve#updateTransformMatrix} has to be called.
873          * @param {JXG.Point} p
874          * @returns {JXG.Point} The given point.
875          */
876         updateTransform: function (p) {
877             var c,
878                 len = this.transformations.length;
879 
880             if (len > 0) {
881                 c = Mat.matVecMult(this.transformMat, p.usrCoords);
882                 p.setCoordinates(Const.COORDS_BY_USER, c, false, true);
883             }
884 
885             return p;
886         },
887 
888         /**
889          * Add transformations to this curve.
890          * @param {JXG.Transformation|Array} transform Either one {@link JXG.Transformation} or an array of {@link JXG.Transformation}s.
891          * @returns {JXG.Curve} Reference to the curve object.
892          */
893         addTransform: function (transform) {
894             var i,
895                 list = Type.isArray(transform) ? transform : [transform],
896                 len = list.length;
897 
898             for (i = 0; i < len; i++) {
899                 this.transformations.push(list[i]);
900             }
901 
902             return this;
903         },
904 
905         /**
906          * Generate the method curve.X() in case curve.dataX is an array
907          * and generate the method curve.Y() in case curve.dataY is an array.
908          * @private
909          * @param {String} which Either 'X' or 'Y'
910          * @returns {function}
911          **/
912         interpolationFunctionFromArray: function (which) {
913             var data = "data" + which,
914                 that = this;
915 
916             return function (t, suspendedUpdate) {
917                 var i,
918                     j,
919                     t0,
920                     t1,
921                     arr = that[data],
922                     len = arr.length,
923                     last,
924                     f = [];
925 
926                 if (isNaN(t)) {
927                     return NaN;
928                 }
929 
930                 if (t < 0) {
931                     if (Type.isFunction(arr[0])) {
932                         return arr[0]();
933                     }
934 
935                     return arr[0];
936                 }
937 
938                 if (that.bezierDegree === 3) {
939                     last = (len - 1) / 3;
940 
941                     if (t >= last) {
942                         if (Type.isFunction(arr[arr.length - 1])) {
943                             return arr[arr.length - 1]();
944                         }
945 
946                         return arr[arr.length - 1];
947                     }
948 
949                     i = Math.floor(t) * 3;
950                     t0 = t % 1;
951                     t1 = 1 - t0;
952 
953                     for (j = 0; j < 4; j++) {
954                         if (Type.isFunction(arr[i + j])) {
955                             f[j] = arr[i + j]();
956                         } else {
957                             f[j] = arr[i + j];
958                         }
959                     }
960 
961                     return (
962                         t1 * t1 * (t1 * f[0] + 3 * t0 * f[1]) +
963                         (3 * t1 * f[2] + t0 * f[3]) * t0 * t0
964                     );
965                 }
966 
967                 if (t > len - 2) {
968                     i = len - 2;
969                 } else {
970                     i = parseInt(Math.floor(t), 10);
971                 }
972 
973                 if (i === t) {
974                     if (Type.isFunction(arr[i])) {
975                         return arr[i]();
976                     }
977                     return arr[i];
978                 }
979 
980                 for (j = 0; j < 2; j++) {
981                     if (Type.isFunction(arr[i + j])) {
982                         f[j] = arr[i + j]();
983                     } else {
984                         f[j] = arr[i + j];
985                     }
986                 }
987                 return f[0] + (f[1] - f[0]) * (t - i);
988             };
989         },
990 
991         /**
992          * Converts the JavaScript/JessieCode/GEONExT syntax of the defining function term into JavaScript.
993          * New methods X() and Y() for the Curve object are generated, further
994          * new methods for minX() and maxX().
995          * If mi or ma are not supplied, default functions are set.
996          *
997          * @param {String} varname Name of the parameter in xterm and yterm, e.g. 'x' or 't'
998          * @param {String|Number|Function|Array} xterm Term for the x coordinate. Can also be an array consisting of discrete values.
999          * @param {String|Number|Function|Array} yterm Term for the y coordinate. Can also be an array consisting of discrete values.
1000          * @param {String|Number|Function} [mi] Lower bound on the parameter
1001          * @param {String|Number|Function} [ma] Upper bound on the parameter
1002          * @see JXG.GeonextParser.geonext2JS
1003          */
1004         generateTerm: function (varname, xterm, yterm, mi, ma) {
1005             var fx, fy;
1006 
1007             // Generate the methods X() and Y()
1008             if (Type.isArray(xterm)) {
1009                 // Discrete data
1010                 this.dataX = xterm;
1011 
1012                 this.numberPoints = this.dataX.length;
1013                 this.X = this.interpolationFunctionFromArray.apply(this, ["X"]);
1014                 this.visProp.curvetype = "plot";
1015                 this.isDraggable = true;
1016             } else {
1017                 // Continuous data
1018                 this.X = Type.createFunction(xterm, this.board, varname);
1019                 if (Type.isString(xterm)) {
1020                     this.visProp.curvetype = "functiongraph";
1021                 } else if (Type.isFunction(xterm) || Type.isNumber(xterm)) {
1022                     this.visProp.curvetype = "parameter";
1023                 }
1024 
1025                 this.isDraggable = true;
1026             }
1027 
1028             if (Type.isArray(yterm)) {
1029                 this.dataY = yterm;
1030                 this.Y = this.interpolationFunctionFromArray.apply(this, ["Y"]);
1031             } else {
1032                 this.Y = Type.createFunction(yterm, this.board, varname);
1033             }
1034 
1035             /**
1036              * Polar form
1037              * Input data is function xterm() and offset coordinates yterm
1038              */
1039             if (Type.isFunction(xterm) && Type.isArray(yterm)) {
1040                 // Xoffset, Yoffset
1041                 fx = Type.createFunction(yterm[0], this.board, "");
1042                 fy = Type.createFunction(yterm[1], this.board, "");
1043 
1044                 this.X = function (phi) {
1045                     return xterm(phi) * Math.cos(phi) + fx();
1046                 };
1047                 this.X.deps = fx.deps;
1048 
1049                 this.Y = function (phi) {
1050                     return xterm(phi) * Math.sin(phi) + fy();
1051                 };
1052                 this.Y.deps = fy.deps;
1053 
1054                 this.visProp.curvetype = "polar";
1055             }
1056 
1057             // Set the upper and lower bounds for the parameter of the curve.
1058             // If not defined, reset the bounds to the default values
1059             // given in Curve.prototype.minX, Curve.prototype.maxX
1060             if (Type.exists(mi)) {
1061                 this.minX = Type.createFunction(mi, this.board, "");
1062             } else {
1063                 delete this.minX;
1064             }
1065             if (Type.exists(ma)) {
1066                 this.maxX = Type.createFunction(ma, this.board, "");
1067             } else {
1068                 delete this.maxX;
1069             }
1070 
1071             this.addParentsFromJCFunctions([this.X, this.Y, this.minX, this.maxX]);
1072         },
1073 
1074         /**
1075          * Finds dependencies in a given term and notifies the parents by adding the
1076          * dependent object to the found objects child elements.
1077          * @param {String} contentStr String containing dependencies for the given object.
1078          */
1079         notifyParents: function (contentStr) {
1080             var fstr,
1081                 dep,
1082                 isJessieCode = false,
1083                 obj;
1084 
1085             // Read dependencies found by the JessieCode parser
1086             obj = { xterm: 1, yterm: 1 };
1087             for (fstr in obj) {
1088                 if (
1089                     obj.hasOwnProperty(fstr) &&
1090                     this.hasOwnProperty(fstr) &&
1091                     this[fstr].origin
1092                 ) {
1093                     isJessieCode = true;
1094                     for (dep in this[fstr].origin.deps) {
1095                         if (this[fstr].origin.deps.hasOwnProperty(dep)) {
1096                             this[fstr].origin.deps[dep].addChild(this);
1097                         }
1098                     }
1099                 }
1100             }
1101 
1102             if (!isJessieCode) {
1103                 GeonextParser.findDependencies(this, contentStr, this.board);
1104             }
1105         },
1106 
1107         // documented in geometry element
1108         getLabelAnchor: function () {
1109             var c,
1110                 x,
1111                 y,
1112                 ax = 0.05 * this.board.canvasWidth,
1113                 ay = 0.05 * this.board.canvasHeight,
1114                 bx = 0.95 * this.board.canvasWidth,
1115                 by = 0.95 * this.board.canvasHeight;
1116 
1117             switch (Type.evaluate(this.visProp.label.position)) {
1118                 case "ulft":
1119                     x = ax;
1120                     y = ay;
1121                     break;
1122                 case "llft":
1123                     x = ax;
1124                     y = by;
1125                     break;
1126                 case "rt":
1127                     x = bx;
1128                     y = 0.5 * by;
1129                     break;
1130                 case "lrt":
1131                     x = bx;
1132                     y = by;
1133                     break;
1134                 case "urt":
1135                     x = bx;
1136                     y = ay;
1137                     break;
1138                 case "top":
1139                     x = 0.5 * bx;
1140                     y = ay;
1141                     break;
1142                 case "bot":
1143                     x = 0.5 * bx;
1144                     y = by;
1145                     break;
1146                 default:
1147                     // includes case 'lft'
1148                     x = ax;
1149                     y = 0.5 * by;
1150             }
1151 
1152             c = new Coords(Const.COORDS_BY_SCREEN, [x, y], this.board, false);
1153             return Geometry.projectCoordsToCurve(
1154                 c.usrCoords[1],
1155                 c.usrCoords[2],
1156                 0,
1157                 this,
1158                 this.board
1159             )[0];
1160         },
1161 
1162         // documented in geometry element
1163         cloneToBackground: function () {
1164             var er,
1165                 copy = {
1166                     id: this.id + "T" + this.numTraces,
1167                     elementClass: Const.OBJECT_CLASS_CURVE,
1168 
1169                     points: this.points.slice(0),
1170                     bezierDegree: this.bezierDegree,
1171                     numberPoints: this.numberPoints,
1172                     board: this.board,
1173                     visProp: Type.deepCopy(this.visProp, this.visProp.traceattributes, true)
1174                 };
1175 
1176             copy.visProp.layer = this.board.options.layer.trace;
1177             copy.visProp.curvetype = this.visProp.curvetype;
1178             this.numTraces++;
1179 
1180             Type.clearVisPropOld(copy);
1181             copy.visPropCalc = {
1182                 visible: Type.evaluate(copy.visProp.visible)
1183             };
1184             er = this.board.renderer.enhancedRendering;
1185             this.board.renderer.enhancedRendering = true;
1186             this.board.renderer.drawCurve(copy);
1187             this.board.renderer.enhancedRendering = er;
1188             this.traces[copy.id] = copy.rendNode;
1189 
1190             return this;
1191         },
1192 
1193         // Already documented in GeometryElement
1194         bounds: function () {
1195             var minX = Infinity,
1196                 maxX = -Infinity,
1197                 minY = Infinity,
1198                 maxY = -Infinity,
1199                 l = this.points.length,
1200                 i,
1201                 bezier,
1202                 up;
1203 
1204             if (this.bezierDegree === 3) {
1205                 // Add methods X(), Y()
1206                 for (i = 0; i < l; i++) {
1207                     this.points[i].X = Type.bind(function () {
1208                         return this.usrCoords[1];
1209                     }, this.points[i]);
1210                     this.points[i].Y = Type.bind(function () {
1211                         return this.usrCoords[2];
1212                     }, this.points[i]);
1213                 }
1214                 bezier = Numerics.bezier(this.points);
1215                 up = bezier[3]();
1216                 minX = Numerics.fminbr(
1217                     function (t) {
1218                         return bezier[0](t);
1219                     },
1220                     [0, up]
1221                 );
1222                 maxX = Numerics.fminbr(
1223                     function (t) {
1224                         return -bezier[0](t);
1225                     },
1226                     [0, up]
1227                 );
1228                 minY = Numerics.fminbr(
1229                     function (t) {
1230                         return bezier[1](t);
1231                     },
1232                     [0, up]
1233                 );
1234                 maxY = Numerics.fminbr(
1235                     function (t) {
1236                         return -bezier[1](t);
1237                     },
1238                     [0, up]
1239                 );
1240 
1241                 minX = bezier[0](minX);
1242                 maxX = bezier[0](maxX);
1243                 minY = bezier[1](minY);
1244                 maxY = bezier[1](maxY);
1245                 return [minX, maxY, maxX, minY];
1246             }
1247 
1248             // Linear segments
1249             for (i = 0; i < l; i++) {
1250                 if (minX > this.points[i].usrCoords[1]) {
1251                     minX = this.points[i].usrCoords[1];
1252                 }
1253 
1254                 if (maxX < this.points[i].usrCoords[1]) {
1255                     maxX = this.points[i].usrCoords[1];
1256                 }
1257 
1258                 if (minY > this.points[i].usrCoords[2]) {
1259                     minY = this.points[i].usrCoords[2];
1260                 }
1261 
1262                 if (maxY < this.points[i].usrCoords[2]) {
1263                     maxY = this.points[i].usrCoords[2];
1264                 }
1265             }
1266 
1267             return [minX, maxY, maxX, minY];
1268         },
1269 
1270         // documented in element.js
1271         getParents: function () {
1272             var p = [this.xterm, this.yterm, this.minX(), this.maxX()];
1273 
1274             if (this.parents.length !== 0) {
1275                 p = this.parents;
1276             }
1277 
1278             return p;
1279         },
1280 
1281         /**
1282          * Shift the curve by the vector 'where'.
1283          *
1284          * @param {Array} where Array containing the x and y coordinate of the target location.
1285          * @returns {JXG.Curve} Reference to itself.
1286          */
1287         moveTo: function (where) {
1288             // TODO add animation
1289             var delta = [],
1290                 p;
1291             if (this.points.length > 0 && !Type.evaluate(this.visProp.fixed)) {
1292                 p = this.points[0];
1293                 if (where.length === 3) {
1294                     delta = [
1295                         where[0] - p.usrCoords[0],
1296                         where[1] - p.usrCoords[1],
1297                         where[2] - p.usrCoords[2]
1298                     ];
1299                 } else {
1300                     delta = [where[0] - p.usrCoords[1], where[1] - p.usrCoords[2]];
1301                 }
1302                 this.setPosition(Const.COORDS_BY_USER, delta);
1303             }
1304             return this;
1305         },
1306 
1307         /**
1308          * If the curve is the result of a transformation applied
1309          * to a continuous curve, the glider projection has to be done
1310          * on the original curve. Otherwise there will be problems
1311          * when changing between high and low precision plotting,
1312          * since there number of points changes.
1313          *
1314          * @private
1315          * @returns {Array} [Boolean, curve]: Array contining 'true' if curve is result of a transformation,
1316          *   and the source curve of the transformation.
1317          */
1318         getTransformationSource: function () {
1319             var isTransformed, curve_org;
1320             if (Type.exists(this._transformationSource)) {
1321                 curve_org = this._transformationSource;
1322                 if (
1323                     curve_org.elementClass === Const.OBJECT_CLASS_CURVE //&&
1324                     //Type.evaluate(curve_org.visProp.curvetype) !== 'plot'
1325                 ) {
1326                     isTransformed = true;
1327                 }
1328             }
1329             return [isTransformed, curve_org];
1330         }
1331 
1332         // See JXG.Math.Geometry.pnpoly
1333         // pnpoly: function (x_in, y_in, coord_type) {
1334         //     var i,
1335         //         j,
1336         //         len,
1337         //         x,
1338         //         y,
1339         //         crds,
1340         //         v = this.points,
1341         //         isIn = false;
1342 
1343         //     if (coord_type === Const.COORDS_BY_USER) {
1344         //         crds = new Coords(Const.COORDS_BY_USER, [x_in, y_in], this.board);
1345         //         x = crds.scrCoords[1];
1346         //         y = crds.scrCoords[2];
1347         //     } else {
1348         //         x = x_in;
1349         //         y = y_in;
1350         //     }
1351 
1352         //     len = this.points.length;
1353         //     for (i = 0, j = len - 2; i < len - 1; j = i++) {
1354         //         if (
1355         //             v[i].scrCoords[2] > y !== v[j].scrCoords[2] > y &&
1356         //             x <
1357         //                 ((v[j].scrCoords[1] - v[i].scrCoords[1]) * (y - v[i].scrCoords[2])) /
1358         //                     (v[j].scrCoords[2] - v[i].scrCoords[2]) +
1359         //                     v[i].scrCoords[1]
1360         //         ) {
1361         //             isIn = !isIn;
1362         //         }
1363         //     }
1364 
1365         //     return isIn;
1366         // }
1367     }
1368 );
1369 
1370 /**
1371  * @class  This element is used to provide a constructor for curve, which is just a wrapper for element {@link Curve}.
1372  * A curve is a mapping from R to R^2. t mapsto (x(t),y(t)). The graph is drawn for t in the interval [a,b].
1373  * <p>
1374  * The following types of curves can be plotted:
1375  * <ul>
1376  *  <li> parametric curves: t mapsto (x(t),y(t)), where x() and y() are univariate functions.
1377  *  <li> polar curves: curves commonly written with polar equations like spirals and cardioids.
1378  *  <li> data plots: plot line segments through a given list of coordinates.
1379  * </ul>
1380  * @pseudo
1381  * @name Curve
1382  * @augments JXG.Curve
1383  * @constructor
1384  * @type Object
1385  * @description JXG.Curve
1386 
1387  * @param {function,number_function,number_function,number_function,number}  x,y,a_,b_ Parent elements for Parametric Curves.
1388  *                     <p>
1389  *                     x describes the x-coordinate of the curve. It may be a function term in one variable, e.g. x(t).
1390  *                     In case of x being of type number, x(t) is set to  a constant function.
1391  *                     this function at the values of the array.
1392  *                     </p>
1393  *                     <p>
1394  *                     y describes the y-coordinate of the curve. In case of a number, y(t) is set to the constant function
1395  *                     returning this number.
1396  *                     </p>
1397  *                     <p>
1398  *                     Further parameters are an optional number or function for the left interval border a,
1399  *                     and an optional number or function for the right interval border b.
1400  *                     </p>
1401  *                     <p>
1402  *                     Default values are a=-10 and b=10.
1403  *                     </p>
1404  *
1405  * @param {array_array,function,number}
1406  *
1407  * @description x,y Parent elements for Data Plots.
1408  *                     <p>
1409  *                     x and y are arrays contining the x and y coordinates of the data points which are connected by
1410  *                     line segments. The individual entries of x and y may also be functions.
1411  *                     In case of x being an array the curve type is data plot, regardless of the second parameter and
1412  *                     if additionally the second parameter y is a function term the data plot evaluates.
1413  *                     </p>
1414  * @param {function_array,function,number_function,number_function,number}
1415  * @description r,offset_,a_,b_ Parent elements for Polar Curves.
1416  *                     <p>
1417  *                     The first parameter is a function term r(phi) describing the polar curve.
1418  *                     </p>
1419  *                     <p>
1420  *                     The second parameter is the offset of the curve. It has to be
1421  *                     an array containing numbers or functions describing the offset. Default value is the origin [0,0].
1422  *                     </p>
1423  *                     <p>
1424  *                     Further parameters are an optional number or function for the left interval border a,
1425  *                     and an optional number or function for the right interval border b.
1426  *                     </p>
1427  *                     <p>
1428  *                     Default values are a=-10 and b=10.
1429  *                     </p>
1430  * <p>
1431  * Additionally, a curve can be created by providing a curve and a transformation (or an array of transformations).
1432  * The result is a curve which is the transformation of the supplied curve.
1433  *
1434  * @see JXG.Curve
1435  * @example
1436  * // Parametric curve
1437  * // Create a curve of the form (t-sin(t), 1-cos(t), i.e.
1438  * // the cycloid curve.
1439  *   var graph = board.create('curve',
1440  *                        [function(t){ return t-Math.sin(t);},
1441  *                         function(t){ return 1-Math.cos(t);},
1442  *                         0, 2*Math.PI]
1443  *                     );
1444  * </pre><div class="jxgbox" id="JXGaf9f818b-f3b6-4c4d-8c4c-e4a4078b726d" style="width: 300px; height: 300px;"></div>
1445  * <script type="text/javascript">
1446  *   var c1_board = JXG.JSXGraph.initBoard('JXGaf9f818b-f3b6-4c4d-8c4c-e4a4078b726d', {boundingbox: [-1, 5, 7, -1], axis: true, showcopyright: false, shownavigation: false});
1447  *   var graph1 = c1_board.create('curve', [function(t){ return t-Math.sin(t);},function(t){ return 1-Math.cos(t);},0, 2*Math.PI]);
1448  * </script><pre>
1449  * @example
1450  * // Data plots
1451  * // Connect a set of points given by coordinates with dashed line segments.
1452  * // The x- and y-coordinates of the points are given in two separate
1453  * // arrays.
1454  *   var x = [0,1,2,3,4,5,6,7,8,9];
1455  *   var y = [9.2,1.3,7.2,-1.2,4.0,5.3,0.2,6.5,1.1,0.0];
1456  *   var graph = board.create('curve', [x,y], {dash:2});
1457  * </pre><div class="jxgbox" id="JXG7dcbb00e-b6ff-481d-b4a8-887f5d8c6a83" style="width: 300px; height: 300px;"></div>
1458  * <script type="text/javascript">
1459  *   var c3_board = JXG.JSXGraph.initBoard('JXG7dcbb00e-b6ff-481d-b4a8-887f5d8c6a83', {boundingbox: [-1,10,10,-1], axis: true, showcopyright: false, shownavigation: false});
1460  *   var x = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
1461  *   var y = [9.2, 1.3, 7.2, -1.2, 4.0, 5.3, 0.2, 6.5, 1.1, 0.0];
1462  *   var graph3 = c3_board.create('curve', [x,y], {dash:2});
1463  * </script><pre>
1464  * @example
1465  * // Polar plot
1466  * // Create a curve with the equation r(phi)= a*(1+phi), i.e.
1467  * // a cardioid.
1468  *   var a = board.create('slider',[[0,2],[2,2],[0,1,2]]);
1469  *   var graph = board.create('curve',
1470  *                        [function(phi){ return a.Value()*(1-Math.cos(phi));},
1471  *                         [1,0],
1472  *                         0, 2*Math.PI],
1473  *                         {curveType: 'polar'}
1474  *                     );
1475  * </pre><div class="jxgbox" id="JXGd0bc7a2a-8124-45ca-a6e7-142321a8f8c2" style="width: 300px; height: 300px;"></div>
1476  * <script type="text/javascript">
1477  *   var c2_board = JXG.JSXGraph.initBoard('JXGd0bc7a2a-8124-45ca-a6e7-142321a8f8c2', {boundingbox: [-3,3,3,-3], axis: true, showcopyright: false, shownavigation: false});
1478  *   var a = c2_board.create('slider',[[0,2],[2,2],[0,1,2]]);
1479  *   var graph2 = c2_board.create('curve', [function(phi){ return a.Value()*(1-Math.cos(phi));}, [1,0], 0, 2*Math.PI], {curveType: 'polar'});
1480  * </script><pre>
1481  *
1482  * @example
1483  *  // Draggable Bezier curve
1484  *  var col, p, c;
1485  *  col = 'blue';
1486  *  p = [];
1487  *  p.push(board.create('point',[-2, -1 ], {size: 5, strokeColor:col, fillColor:col}));
1488  *  p.push(board.create('point',[1, 2.5 ], {size: 5, strokeColor:col, fillColor:col}));
1489  *  p.push(board.create('point',[-1, -2.5 ], {size: 5, strokeColor:col, fillColor:col}));
1490  *  p.push(board.create('point',[2, -2], {size: 5, strokeColor:col, fillColor:col}));
1491  *
1492  *  c = board.create('curve', JXG.Math.Numerics.bezier(p),
1493  *              {strokeColor:'red', name:"curve", strokeWidth:5, fixed: false}); // Draggable curve
1494  *  c.addParents(p);
1495  * </pre><div class="jxgbox" id="JXG7bcc6280-f6eb-433e-8281-c837c3387849" style="width: 300px; height: 300px;"></div>
1496  * <script type="text/javascript">
1497  * (function(){
1498  *  var board, col, p, c;
1499  *  board = JXG.JSXGraph.initBoard('JXG7bcc6280-f6eb-433e-8281-c837c3387849', {boundingbox: [-3,3,3,-3], axis: true, showcopyright: false, shownavigation: false});
1500  *  col = 'blue';
1501  *  p = [];
1502  *  p.push(board.create('point',[-2, -1 ], {size: 5, strokeColor:col, fillColor:col}));
1503  *  p.push(board.create('point',[1, 2.5 ], {size: 5, strokeColor:col, fillColor:col}));
1504  *  p.push(board.create('point',[-1, -2.5 ], {size: 5, strokeColor:col, fillColor:col}));
1505  *  p.push(board.create('point',[2, -2], {size: 5, strokeColor:col, fillColor:col}));
1506  *
1507  *  c = board.create('curve', JXG.Math.Numerics.bezier(p),
1508  *              {strokeColor:'red', name:"curve", strokeWidth:5, fixed: false}); // Draggable curve
1509  *  c.addParents(p);
1510  * })();
1511  * </script><pre>
1512  *
1513  * @example
1514  *         // The curve cu2 is the reflection of cu1 against line li
1515  *         var li = board.create('line', [1,1,1], {strokeColor: '#aaaaaa'});
1516  *         var reflect = board.create('transform', [li], {type: 'reflect'});
1517  *         var cu1 = board.create('curve', [[-1, -1, -0.5, -1, -1, -0.5], [-3, -2, -2, -2, -2.5, -2.5]]);
1518  *         var cu2 = board.create('curve', [cu1, reflect], {strokeColor: 'red'});
1519  *
1520  * </pre><div id="JXG866dc7a2-d448-11e7-93b3-901b0e1b8723" class="jxgbox" style="width: 300px; height: 300px;"></div>
1521  * <script type="text/javascript">
1522  *     (function() {
1523  *         var board = JXG.JSXGraph.initBoard('JXG866dc7a2-d448-11e7-93b3-901b0e1b8723',
1524  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
1525  *             var li = board.create('line', [1,1,1], {strokeColor: '#aaaaaa'});
1526  *             var reflect = board.create('transform', [li], {type: 'reflect'});
1527  *             var cu1 = board.create('curve', [[-1, -1, -0.5, -1, -1, -0.5], [-3, -2, -2, -2, -2.5, -2.5]]);
1528  *             var cu2 = board.create('curve', [cu1, reflect], {strokeColor: 'red'});
1529  *
1530  *     })();
1531  *
1532  * </script><pre>
1533  */
1534 JXG.createCurve = function (board, parents, attributes) {
1535     var obj,
1536         cu,
1537         attr = Type.copyAttributes(attributes, board.options, "curve");
1538 
1539     obj = board.select(parents[0], true);
1540     if (
1541         Type.isTransformationOrArray(parents[1]) &&
1542         Type.isObject(obj) &&
1543         (obj.type === Const.OBJECT_TYPE_CURVE ||
1544             obj.type === Const.OBJECT_TYPE_ANGLE ||
1545             obj.type === Const.OBJECT_TYPE_ARC ||
1546             obj.type === Const.OBJECT_TYPE_CONIC ||
1547             obj.type === Const.OBJECT_TYPE_SECTOR)
1548     ) {
1549         if (obj.type === Const.OBJECT_TYPE_SECTOR) {
1550             attr = Type.copyAttributes(attributes, board.options, "sector");
1551         } else if (obj.type === Const.OBJECT_TYPE_ARC) {
1552             attr = Type.copyAttributes(attributes, board.options, "arc");
1553         } else if (obj.type === Const.OBJECT_TYPE_ANGLE) {
1554             if (!Type.exists(attributes.withLabel)) {
1555                 attributes.withLabel = false;
1556             }
1557             attr = Type.copyAttributes(attributes, board.options, "angle");
1558         } else {
1559             attr = Type.copyAttributes(attributes, board.options, "curve");
1560         }
1561         attr = Type.copyAttributes(attr, board.options, "curve");
1562 
1563         cu = new JXG.Curve(board, ["x", [], []], attr);
1564         /**
1565          * @class
1566          * @ignore
1567          */
1568         cu.updateDataArray = function () {
1569             var i,
1570                 le = obj.numberPoints;
1571             this.bezierDegree = obj.bezierDegree;
1572             this.dataX = [];
1573             this.dataY = [];
1574             for (i = 0; i < le; i++) {
1575                 this.dataX.push(obj.points[i].usrCoords[1]);
1576                 this.dataY.push(obj.points[i].usrCoords[2]);
1577             }
1578             return this;
1579         };
1580         cu.addTransform(parents[1]);
1581         obj.addChild(cu);
1582         cu.setParents([obj]);
1583         cu._transformationSource = obj;
1584 
1585         return cu;
1586     }
1587     attr = Type.copyAttributes(attributes, board.options, "curve");
1588     return new JXG.Curve(board, ["x"].concat(parents), attr);
1589 };
1590 
1591 JXG.registerElement("curve", JXG.createCurve);
1592 
1593 /**
1594  * @class This element is used to provide a constructor for functiongraph,
1595  * which is just a wrapper for element {@link Curve} with {@link JXG.Curve#X}()
1596  * set to x. The graph is drawn for x in the interval [a,b].
1597  * @pseudo
1598  * @name Functiongraph
1599  * @augments JXG.Curve
1600  * @constructor
1601  * @type JXG.Curve
1602  * @param {function_number,function_number,function} f,a_,b_ Parent elements are a function term f(x) describing the function graph.
1603  *         <p>
1604  *         Further, an optional number or function for the left interval border a,
1605  *         and an optional number or function for the right interval border b.
1606  *         <p>
1607  *         Default values are a=-10 and b=10.
1608  * @see JXG.Curve
1609  * @example
1610  * // Create a function graph for f(x) = 0.5*x*x-2*x
1611  *   var graph = board.create('functiongraph',
1612  *                        [function(x){ return 0.5*x*x-2*x;}, -2, 4]
1613  *                     );
1614  * </pre><div class="jxgbox" id="JXGefd432b5-23a3-4846-ac5b-b471e668b437" style="width: 300px; height: 300px;"></div>
1615  * <script type="text/javascript">
1616  *   var alex1_board = JXG.JSXGraph.initBoard('JXGefd432b5-23a3-4846-ac5b-b471e668b437', {boundingbox: [-3, 7, 5, -3], axis: true, showcopyright: false, shownavigation: false});
1617  *   var graph = alex1_board.create('functiongraph', [function(x){ return 0.5*x*x-2*x;}, -2, 4]);
1618  * </script><pre>
1619  * @example
1620  * // Create a function graph for f(x) = 0.5*x*x-2*x with variable interval
1621  *   var s = board.create('slider',[[0,4],[3,4],[-2,4,5]]);
1622  *   var graph = board.create('functiongraph',
1623  *                        [function(x){ return 0.5*x*x-2*x;},
1624  *                         -2,
1625  *                         function(){return s.Value();}]
1626  *                     );
1627  * </pre><div class="jxgbox" id="JXG4a203a84-bde5-4371-ad56-44619690bb50" style="width: 300px; height: 300px;"></div>
1628  * <script type="text/javascript">
1629  *   var alex2_board = JXG.JSXGraph.initBoard('JXG4a203a84-bde5-4371-ad56-44619690bb50', {boundingbox: [-3, 7, 5, -3], axis: true, showcopyright: false, shownavigation: false});
1630  *   var s = alex2_board.create('slider',[[0,4],[3,4],[-2,4,5]]);
1631  *   var graph = alex2_board.create('functiongraph', [function(x){ return 0.5*x*x-2*x;}, -2, function(){return s.Value();}]);
1632  * </script><pre>
1633  */
1634 JXG.createFunctiongraph = function (board, parents, attributes) {
1635     var attr,
1636         par = ["x", "x"].concat(parents); // variable name and identity function for x-coordinate
1637         // par = ["x", function(x) { return x; }].concat(parents);
1638 
1639     attr = Type.copyAttributes(attributes, board.options, "functiongraph");
1640     attr = Type.copyAttributes(attr, board.options, "curve");
1641     attr.curvetype = "functiongraph";
1642     return new JXG.Curve(board, par, attr);
1643 };
1644 
1645 JXG.registerElement("functiongraph", JXG.createFunctiongraph);
1646 JXG.registerElement("plot", JXG.createFunctiongraph);
1647 
1648 /**
1649  * @class This element is used to provide a constructor for (natural) cubic spline curves.
1650  * Create a dynamic spline interpolated curve given by sample points p_1 to p_n.
1651  * @pseudo
1652  * @name Spline
1653  * @augments JXG.Curve
1654  * @constructor
1655  * @type JXG.Curve
1656  * @param {JXG.Board} board Reference to the board the spline is drawn on.
1657  * @param {Array} parents Array of points the spline interpolates. This can be
1658  *   <ul>
1659  *   <li> an array of JSXGraph points</li>
1660  *   <li> an array of coordinate pairs</li>
1661  *   <li> an array of functions returning coordinate pairs</li>
1662  *   <li> an array consisting of an array with x-coordinates and an array of y-coordinates</li>
1663  *   </ul>
1664  *   All individual entries of coordinates arrays may be numbers or functions returning numbers.
1665  * @param {Object} attributes Define color, width, ... of the spline
1666  * @returns {JXG.Curve} Returns reference to an object of type JXG.Curve.
1667  * @see JXG.Curve
1668  * @example
1669  *
1670  * var p = [];
1671  * p[0] = board.create('point', [-2,2], {size: 4, face: 'o'});
1672  * p[1] = board.create('point', [0,-1], {size: 4, face: 'o'});
1673  * p[2] = board.create('point', [2,0], {size: 4, face: 'o'});
1674  * p[3] = board.create('point', [4,1], {size: 4, face: 'o'});
1675  *
1676  * var c = board.create('spline', p, {strokeWidth:3});
1677  * </pre><div id="JXG6c197afc-e482-11e5-b1bf-901b0e1b8723" style="width: 300px; height: 300px;"></div>
1678  * <script type="text/javascript">
1679  *     (function() {
1680  *         var board = JXG.JSXGraph.initBoard('JXG6c197afc-e482-11e5-b1bf-901b0e1b8723',
1681  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
1682  *
1683  *     var p = [];
1684  *     p[0] = board.create('point', [-2,2], {size: 4, face: 'o'});
1685  *     p[1] = board.create('point', [0,-1], {size: 4, face: 'o'});
1686  *     p[2] = board.create('point', [2,0], {size: 4, face: 'o'});
1687  *     p[3] = board.create('point', [4,1], {size: 4, face: 'o'});
1688  *
1689  *     var c = board.create('spline', p, {strokeWidth:3});
1690  *     })();
1691  *
1692  * </script><pre>
1693  *
1694  */
1695 JXG.createSpline = function (board, parents, attributes) {
1696     var el, funcs, ret;
1697 
1698     funcs = function () {
1699         var D,
1700             x = [],
1701             y = [];
1702 
1703         return [
1704             function (t, suspended) {
1705                 // Function term
1706                 var i, j, c;
1707 
1708                 if (!suspended) {
1709                     x = [];
1710                     y = [];
1711 
1712                     // given as [x[], y[]]
1713                     if (
1714                         parents.length === 2 &&
1715                         Type.isArray(parents[0]) &&
1716                         Type.isArray(parents[1]) &&
1717                         parents[0].length === parents[1].length
1718                     ) {
1719                         for (i = 0; i < parents[0].length; i++) {
1720                             if (Type.isFunction(parents[0][i])) {
1721                                 x.push(parents[0][i]());
1722                             } else {
1723                                 x.push(parents[0][i]);
1724                             }
1725 
1726                             if (Type.isFunction(parents[1][i])) {
1727                                 y.push(parents[1][i]());
1728                             } else {
1729                                 y.push(parents[1][i]);
1730                             }
1731                         }
1732                     } else {
1733                         for (i = 0; i < parents.length; i++) {
1734                             if (Type.isPoint(parents[i])) {
1735                                 x.push(parents[i].X());
1736                                 y.push(parents[i].Y());
1737                                 // given as [[x1,y1], [x2, y2], ...]
1738                             } else if (Type.isArray(parents[i]) && parents[i].length === 2) {
1739                                 for (j = 0; j < parents.length; j++) {
1740                                     if (Type.isFunction(parents[j][0])) {
1741                                         x.push(parents[j][0]());
1742                                     } else {
1743                                         x.push(parents[j][0]);
1744                                     }
1745 
1746                                     if (Type.isFunction(parents[j][1])) {
1747                                         y.push(parents[j][1]());
1748                                     } else {
1749                                         y.push(parents[j][1]);
1750                                     }
1751                                 }
1752                             } else if (
1753                                 Type.isFunction(parents[i]) &&
1754                                 parents[i]().length === 2
1755                             ) {
1756                                 c = parents[i]();
1757                                 x.push(c[0]);
1758                                 y.push(c[1]);
1759                             }
1760                         }
1761                     }
1762 
1763                     // The array D has only to be calculated when the position of one or more sample points
1764                     // changes. Otherwise D is always the same for all points on the spline.
1765                     D = Numerics.splineDef(x, y);
1766                 }
1767 
1768                 return Numerics.splineEval(t, x, y, D);
1769             },
1770             // minX()
1771             function () {
1772                 return x[0];
1773             },
1774             //maxX()
1775             function () {
1776                 return x[x.length - 1];
1777             }
1778         ];
1779     };
1780 
1781     attributes = Type.copyAttributes(attributes, board.options, "curve");
1782     attributes.curvetype = "functiongraph";
1783     ret = funcs();
1784     el = new JXG.Curve(board, ["x", "x", ret[0], ret[1], ret[2]], attributes);
1785     el.setParents(parents);
1786     el.elType = "spline";
1787 
1788     return el;
1789 };
1790 
1791 /**
1792  * Register the element type spline at JSXGraph
1793  * @private
1794  */
1795 JXG.registerElement("spline", JXG.createSpline);
1796 
1797 /**
1798  * @class This element is used to provide a constructor for cardinal spline curves.
1799  * Create a dynamic cardinal spline interpolated curve given by sample points p_1 to p_n.
1800  * @pseudo
1801  * @name Cardinalspline
1802  * @augments JXG.Curve
1803  * @constructor
1804  * @type JXG.Curve
1805  * @param {JXG.Board} board Reference to the board the cardinal spline is drawn on.
1806  * @param {Array} parents Array with three entries.
1807  * <p>
1808  *   First entry: Array of points the spline interpolates. This can be
1809  *   <ul>
1810  *   <li> an array of JSXGraph points</li>
1811  *   <li> an array of coordinate pairs</li>
1812  *   <li> an array of functions returning coordinate pairs</li>
1813  *   <li> an array consisting of an array with x-coordinates and an array of y-coordinates</li>
1814  *   </ul>
1815  *   All individual entries of coordinates arrays may be numbers or functions returning numbers.
1816  *   <p>
1817  *   Second entry: tau number or function
1818  *   <p>
1819  *   Third entry: type string containing 'uniform' (default) or 'centripetal'.
1820  * @param {Object} attributes Define color, width, ... of the cardinal spline
1821  * @returns {JXG.Curve} Returns reference to an object of type JXG.Curve.
1822  * @see JXG.Curve
1823  * @example
1824  * //create a cardinal spline out of an array of JXG points with adjustable tension
1825  * //create array of points
1826  * var p1 = board.create('point',[0,0])
1827  * var p2 = board.create('point',[1,4])
1828  * var p3 = board.create('point',[4,5])
1829  * var p4 = board.create('point',[2,3])
1830  * var p5 = board.create('point',[3,0])
1831  * var p = [p1,p2,p3,p4,p5]
1832  *
1833  * // tension
1834  * tau = board.create('slider', [[4,3],[9,3],[0.001,0.5,1]], {name:'tau'});
1835  * c = board.create('curve', JXG.Math.Numerics.CardinalSpline(p, function(){ return tau.Value();}), {strokeWidth:3});
1836  * </pre><div id="JXG6c197afc-e482-11e5-b2af-901b0e1b8723" style="width: 300px; height: 300px;"></div>
1837  * <script type="text/javascript">
1838  *     (function() {
1839  *         var board = JXG.JSXGraph.initBoard('JXG6c197afc-e482-11e5-b2af-901b0e1b8723',
1840  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
1841  *
1842  *     var p = [];
1843  *     p[0] = board.create('point', [-2,2], {size: 4, face: 'o'});
1844  *     p[1] = board.create('point', [0,-1], {size: 4, face: 'o'});
1845  *     p[2] = board.create('point', [2,0], {size: 4, face: 'o'});
1846  *     p[3] = board.create('point', [4,1], {size: 4, face: 'o'});
1847  *
1848  *     var c = board.create('spline', p, {strokeWidth:3});
1849  *     })();
1850  *
1851  * </script><pre>
1852  */
1853 JXG.createCardinalSpline = function (board, parents, attributes) {
1854     var el,
1855         getPointLike,
1856         points,
1857         tau,
1858         type,
1859         p,
1860         q,
1861         i,
1862         le,
1863         splineArr,
1864         errStr = "\nPossible parent types: [points:array, tau:number|function, type:string]";
1865 
1866     if (!Type.exists(parents[0]) || !Type.isArray(parents[0])) {
1867         throw new Error(
1868             "JSXGraph: JXG.createCardinalSpline: argument 1 'points' has to be array of points or coordinate pairs" +
1869                 errStr
1870         );
1871     }
1872     if (
1873         !Type.exists(parents[1]) ||
1874         (!Type.isNumber(parents[1]) && !Type.isFunction(parents[1]))
1875     ) {
1876         throw new Error(
1877             "JSXGraph: JXG.createCardinalSpline: argument 2 'tau' has to be number between [0,1] or function'" +
1878                 errStr
1879         );
1880     }
1881     if (!Type.exists(parents[2]) || !Type.isString(parents[2])) {
1882         throw new Error(
1883             "JSXGraph: JXG.createCardinalSpline: argument 3 'type' has to be string 'uniform' or 'centripetal'" +
1884                 errStr
1885         );
1886     }
1887 
1888     attributes = Type.copyAttributes(attributes, board.options, "curve");
1889     attributes = Type.copyAttributes(attributes, board.options, "cardinalspline");
1890     attributes.curvetype = "parameter";
1891 
1892     p = parents[0];
1893     q = [];
1894 
1895     // Given as [x[], y[]]
1896     if (
1897         !attributes.isarrayofcoordinates &&
1898         p.length === 2 &&
1899         Type.isArray(p[0]) &&
1900         Type.isArray(p[1]) &&
1901         p[0].length === p[1].length
1902     ) {
1903         for (i = 0; i < p[0].length; i++) {
1904             q[i] = [];
1905             if (Type.isFunction(p[0][i])) {
1906                 q[i].push(p[0][i]());
1907             } else {
1908                 q[i].push(p[0][i]);
1909             }
1910 
1911             if (Type.isFunction(p[1][i])) {
1912                 q[i].push(p[1][i]());
1913             } else {
1914                 q[i].push(p[1][i]);
1915             }
1916         }
1917     } else {
1918         // given as [[x0, y0], [x1, y1], point, ...]
1919         for (i = 0; i < p.length; i++) {
1920             if (Type.isString(p[i])) {
1921                 q.push(board.select(p[i]));
1922             } else if (Type.isPoint(p[i])) {
1923                 q.push(p[i]);
1924                 // given as [[x0,y0], [x1, y2], ...]
1925             } else if (Type.isArray(p[i]) && p[i].length === 2) {
1926                 q[i] = [];
1927                 if (Type.isFunction(p[i][0])) {
1928                     q[i].push(p[i][0]());
1929                 } else {
1930                     q[i].push(p[i][0]);
1931                 }
1932 
1933                 if (Type.isFunction(p[i][1])) {
1934                     q[i].push(p[i][1]());
1935                 } else {
1936                     q[i].push(p[i][1]);
1937                 }
1938             } else if (Type.isFunction(p[i]) && p[i]().length === 2) {
1939                 q.push(parents[i]());
1940             }
1941         }
1942     }
1943 
1944     if (attributes.createpoints === true) {
1945         points = Type.providePoints(board, q, attributes, "cardinalspline", ["points"]);
1946     } else {
1947         points = [];
1948 
1949         /**
1950          * @ignore
1951          */
1952         getPointLike = function (ii) {
1953             return {
1954                 X: function () {
1955                     return q[ii][0];
1956                 },
1957                 Y: function () {
1958                     return q[ii][1];
1959                 },
1960                 Dist: function (p) {
1961                     var dx = this.X() - p.X(),
1962                         dy = this.Y() - p.Y();
1963 
1964                     return Mat.hypot(dx, dy);
1965                 }
1966             };
1967         };
1968 
1969         for (i = 0; i < q.length; i++) {
1970             if (Type.isPoint(q[i])) {
1971                 points.push(q[i]);
1972             } else {
1973                 points.push(getPointLike(i));
1974             }
1975         }
1976     }
1977 
1978     tau = parents[1];
1979     type = parents[2];
1980 
1981     splineArr = ["x"].concat(Numerics.CardinalSpline(points, tau, type));
1982 
1983     el = new JXG.Curve(board, splineArr, attributes);
1984     le = points.length;
1985     el.setParents(points);
1986     for (i = 0; i < le; i++) {
1987         p = points[i];
1988         if (Type.isPoint(p)) {
1989             if (Type.exists(p._is_new)) {
1990                 el.addChild(p);
1991                 delete p._is_new;
1992             } else {
1993                 p.addChild(el);
1994             }
1995         }
1996     }
1997     el.elType = "cardinalspline";
1998 
1999     return el;
2000 };
2001 
2002 /**
2003  * Register the element type cardinalspline at JSXGraph
2004  * @private
2005  */
2006 JXG.registerElement("cardinalspline", JXG.createCardinalSpline);
2007 
2008 /**
2009  * @class This element is used to provide a constructor for metapost spline curves.
2010  * Create a dynamic metapost spline interpolated curve given by sample points p_1 to p_n.
2011  * @pseudo
2012  * @name Metapostspline
2013  * @augments JXG.Curve
2014  * @constructor
2015  * @type JXG.Curve
2016  * @param {JXG.Board} board Reference to the board the metapost spline is drawn on.
2017  * @param {Array} parents Array with two entries.
2018  * <p>
2019  *   First entry: Array of points the spline interpolates. This can be
2020  *   <ul>
2021  *   <li> an array of JSXGraph points</li>
2022  *   <li> an object of coordinate pairs</li>
2023  *   <li> an array of functions returning coordinate pairs</li>
2024  *   <li> an array consisting of an array with x-coordinates and an array of y-coordinates</li>
2025  *   </ul>
2026  *   All individual entries of coordinates arrays may be numbers or functions returning numbers.
2027  *   <p>
2028  *   Second entry: JavaScript object containing the control values like tension, direction, curl.
2029  * @param {Object} attributes Define color, width, ... of the metapost spline
2030  * @returns {JXG.Curve} Returns reference to an object of type JXG.Curve.
2031  * @see JXG.Curve
2032  * @example
2033  *     var po = [],
2034  *         attr = {
2035  *             size: 5,
2036  *             color: 'red'
2037  *         },
2038  *         controls;
2039  *
2040  *     var tension = board.create('slider', [[-3, 6], [3, 6], [0, 1, 20]], {name: 'tension'});
2041  *     var curl = board.create('slider', [[-3, 5], [3, 5], [0, 1, 30]], {name: 'curl A, D'});
2042  *     var dir = board.create('slider', [[-3, 4], [3, 4], [-180, 0, 180]], {name: 'direction B'});
2043  *
2044  *     po.push(board.create('point', [-3, -3]));
2045  *     po.push(board.create('point', [0, -3]));
2046  *     po.push(board.create('point', [4, -5]));
2047  *     po.push(board.create('point', [6, -2]));
2048  *
2049  *     var controls = {
2050  *         tension: function() {return tension.Value(); },
2051  *         direction: { 1: function() {return dir.Value(); } },
2052  *         curl: { 0: function() {return curl.Value(); },
2053  *                 3: function() {return curl.Value(); }
2054  *             },
2055  *         isClosed: false
2056  *     };
2057  *
2058  *     // Plot a metapost curve
2059  *     var cu = board.create('metapostspline', [po, controls], {strokeColor: 'blue', strokeWidth: 2});
2060  *
2061  *
2062  * </pre><div id="JXGb8c6ffed-7419-41a3-9e55-3754b2327ae9" class="jxgbox" style="width: 300px; height: 300px;"></div>
2063  * <script type="text/javascript">
2064  *     (function() {
2065  *         var board = JXG.JSXGraph.initBoard('JXGb8c6ffed-7419-41a3-9e55-3754b2327ae9',
2066  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
2067  *         var po = [],
2068  *             attr = {
2069  *                 size: 5,
2070  *                 color: 'red'
2071  *             },
2072  *             controls;
2073  *
2074  *         var tension = board.create('slider', [[-3, 6], [3, 6], [0, 1, 20]], {name: 'tension'});
2075  *         var curl = board.create('slider', [[-3, 5], [3, 5], [0, 1, 30]], {name: 'curl A, D'});
2076  *         var dir = board.create('slider', [[-3, 4], [3, 4], [-180, 0, 180]], {name: 'direction B'});
2077  *
2078  *         po.push(board.create('point', [-3, -3]));
2079  *         po.push(board.create('point', [0, -3]));
2080  *         po.push(board.create('point', [4, -5]));
2081  *         po.push(board.create('point', [6, -2]));
2082  *
2083  *         var controls = {
2084  *             tension: function() {return tension.Value(); },
2085  *             direction: { 1: function() {return dir.Value(); } },
2086  *             curl: { 0: function() {return curl.Value(); },
2087  *                     3: function() {return curl.Value(); }
2088  *                 },
2089  *             isClosed: false
2090  *         };
2091  *
2092  *         // Plot a metapost curve
2093  *         var cu = board.create('metapostspline', [po, controls], {strokeColor: 'blue', strokeWidth: 2});
2094  *
2095  *
2096  *     })();
2097  *
2098  * </script><pre>
2099  *
2100  */
2101 JXG.createMetapostSpline = function (board, parents, attributes) {
2102     var el,
2103         getPointLike,
2104         points,
2105         controls,
2106         p,
2107         q,
2108         i,
2109         le,
2110         errStr = "\nPossible parent types: [points:array, controls:object";
2111 
2112     if (!Type.exists(parents[0]) || !Type.isArray(parents[0])) {
2113         throw new Error(
2114             "JSXGraph: JXG.createMetapostSpline: argument 1 'points' has to be array of points or coordinate pairs" +
2115                 errStr
2116         );
2117     }
2118     if (!Type.exists(parents[1]) || !Type.isObject(parents[1])) {
2119         throw new Error(
2120             "JSXGraph: JXG.createMetapostSpline: argument 2 'controls' has to be a JavaScript object'" +
2121                 errStr
2122         );
2123     }
2124 
2125     attributes = Type.copyAttributes(attributes, board.options, "curve");
2126     attributes = Type.copyAttributes(attributes, board.options, "metapostspline");
2127     attributes.curvetype = "parameter";
2128 
2129     p = parents[0];
2130     q = [];
2131 
2132     // given as [x[], y[]]
2133     if (
2134         !attributes.isarrayofcoordinates &&
2135         p.length === 2 &&
2136         Type.isArray(p[0]) &&
2137         Type.isArray(p[1]) &&
2138         p[0].length === p[1].length
2139     ) {
2140         for (i = 0; i < p[0].length; i++) {
2141             q[i] = [];
2142             if (Type.isFunction(p[0][i])) {
2143                 q[i].push(p[0][i]());
2144             } else {
2145                 q[i].push(p[0][i]);
2146             }
2147 
2148             if (Type.isFunction(p[1][i])) {
2149                 q[i].push(p[1][i]());
2150             } else {
2151                 q[i].push(p[1][i]);
2152             }
2153         }
2154     } else {
2155         // given as [[x0, y0], [x1, y1], point, ...]
2156         for (i = 0; i < p.length; i++) {
2157             if (Type.isString(p[i])) {
2158                 q.push(board.select(p[i]));
2159             } else if (Type.isPoint(p[i])) {
2160                 q.push(p[i]);
2161                 // given as [[x0,y0], [x1, y2], ...]
2162             } else if (Type.isArray(p[i]) && p[i].length === 2) {
2163                 q[i] = [];
2164                 if (Type.isFunction(p[i][0])) {
2165                     q[i].push(p[i][0]());
2166                 } else {
2167                     q[i].push(p[i][0]);
2168                 }
2169 
2170                 if (Type.isFunction(p[i][1])) {
2171                     q[i].push(p[i][1]());
2172                 } else {
2173                     q[i].push(p[i][1]);
2174                 }
2175             } else if (Type.isFunction(p[i]) && p[i]().length === 2) {
2176                 q.push(parents[i]());
2177             }
2178         }
2179     }
2180 
2181     if (attributes.createpoints === true) {
2182         points = Type.providePoints(board, q, attributes, 'metapostspline', ['points']);
2183     } else {
2184         points = [];
2185 
2186         /**
2187          * @ignore
2188          */
2189         getPointLike = function (ii) {
2190             return {
2191                 X: function () {
2192                     return q[ii][0];
2193                 },
2194                 Y: function () {
2195                     return q[ii][1];
2196                 }
2197             };
2198         };
2199 
2200         for (i = 0; i < q.length; i++) {
2201             if (Type.isPoint(q[i])) {
2202                 points.push(q[i]);
2203             } else {
2204                 points.push(getPointLike);
2205             }
2206         }
2207     }
2208 
2209     controls = parents[1];
2210 
2211     el = new JXG.Curve(board, ["t", [], [], 0, p.length - 1], attributes);
2212     /**
2213      * @class
2214      * @ignore
2215      */
2216     el.updateDataArray = function () {
2217         var res,
2218             i,
2219             len = points.length,
2220             p = [];
2221 
2222         for (i = 0; i < len; i++) {
2223             p.push([points[i].X(), points[i].Y()]);
2224         }
2225 
2226         res = Metapost.curve(p, controls);
2227         this.dataX = res[0];
2228         this.dataY = res[1];
2229     };
2230     el.bezierDegree = 3;
2231 
2232     le = points.length;
2233     el.setParents(points);
2234     for (i = 0; i < le; i++) {
2235         if (Type.isPoint(points[i])) {
2236             points[i].addChild(el);
2237         }
2238     }
2239     el.elType = "metapostspline";
2240 
2241     return el;
2242 };
2243 
2244 JXG.registerElement("metapostspline", JXG.createMetapostSpline);
2245 
2246 /**
2247  * @class This element is used to provide a constructor for Riemann sums, which is realized as a special curve.
2248  * The returned element has the method Value() which returns the sum of the areas of the bars.
2249  * <p>
2250  * In case of type "simpson" and "trapezoidal", the horizontal line approximating the function value
2251  * is replaced by a parabola or a secant. IN case of "simpson",
2252  * the parabola is approximated visually by a polygonal chain of fixed step width.
2253  *
2254  * @pseudo
2255  * @name Riemannsum
2256  * @augments JXG.Curve
2257  * @constructor
2258  * @type Curve
2259  * @param {function,array_number,function_string,function_function,number_function,number} f,n,type_,a_,b_ Parent elements of Riemannsum are a
2260  *         Either a function term f(x) describing the function graph which is filled by the Riemann bars, or
2261  *         an array consisting of two functions and the area between is filled by the Riemann bars.
2262  *         <p>
2263  *         n determines the number of bars, it is either a fixed number or a function.
2264  *         <p>
2265  *         type is a string or function returning one of the values:  'left', 'right', 'middle', 'lower', 'upper', 'random', 'simpson', or 'trapezoidal'.
2266  *         Default value is 'left'. "simpson" is Simpson's 1/3 rule.
2267  *         <p>
2268  *         Further parameters are an optional number or function for the left interval border a,
2269  *         and an optional number or function for the right interval border b.
2270  *         <p>
2271  *         Default values are a=-10 and b=10.
2272  * @see JXG.Curve
2273  * @example
2274  * // Create Riemann sums for f(x) = 0.5*x*x-2*x.
2275  *   var s = board.create('slider',[[0,4],[3,4],[0,4,10]],{snapWidth:1});
2276  *   var f = function(x) { return 0.5*x*x-2*x; };
2277  *   var r = board.create('riemannsum',
2278  *               [f, function(){return s.Value();}, 'upper', -2, 5],
2279  *               {fillOpacity:0.4}
2280  *               );
2281  *   var g = board.create('functiongraph',[f, -2, 5]);
2282  *   var t = board.create('text',[-2,-2, function(){ return 'Sum=' + JXG.toFixed(r.Value(), 4); }]);
2283  * </pre><div class="jxgbox" id="JXG940f40cc-2015-420d-9191-c5d83de988cf" style="width: 300px; height: 300px;"></div>
2284  * <script type="text/javascript">
2285  * (function(){
2286  *   var board = JXG.JSXGraph.initBoard('JXG940f40cc-2015-420d-9191-c5d83de988cf', {boundingbox: [-3, 7, 5, -3], axis: true, showcopyright: false, shownavigation: false});
2287  *   var f = function(x) { return 0.5*x*x-2*x; };
2288  *   var s = board.create('slider',[[0,4],[3,4],[0,4,10]],{snapWidth:1});
2289  *   var r = board.create('riemannsum', [f, function(){return s.Value();}, 'upper', -2, 5], {fillOpacity:0.4});
2290  *   var g = board.create('functiongraph', [f, -2, 5]);
2291  *   var t = board.create('text',[-2,-2, function(){ return 'Sum=' + JXG.toFixed(r.Value(), 4); }]);
2292  * })();
2293  * </script><pre>
2294  *
2295  * @example
2296  *   // Riemann sum between two functions
2297  *   var s = board.create('slider',[[0,4],[3,4],[0,4,10]],{snapWidth:1});
2298  *   var g = function(x) { return 0.5*x*x-2*x; };
2299  *   var f = function(x) { return -x*(x-4); };
2300  *   var r = board.create('riemannsum',
2301  *               [[g,f], function(){return s.Value();}, 'lower', 0, 4],
2302  *               {fillOpacity:0.4}
2303  *               );
2304  *   var f = board.create('functiongraph',[f, -2, 5]);
2305  *   var g = board.create('functiongraph',[g, -2, 5]);
2306  *   var t = board.create('text',[-2,-2, function(){ return 'Sum=' + JXG.toFixed(r.Value(), 4); }]);
2307  * </pre><div class="jxgbox" id="JXGf9a7ba38-b50f-4a32-a873-2f3bf9caee79" style="width: 300px; height: 300px;"></div>
2308  * <script type="text/javascript">
2309  * (function(){
2310  *   var board = JXG.JSXGraph.initBoard('JXGf9a7ba38-b50f-4a32-a873-2f3bf9caee79', {boundingbox: [-3, 7, 5, -3], axis: true, showcopyright: false, shownavigation: false});
2311  *   var s = board.create('slider',[[0,4],[3,4],[0,4,10]],{snapWidth:1});
2312  *   var g = function(x) { return 0.5*x*x-2*x; };
2313  *   var f = function(x) { return -x*(x-4); };
2314  *   var r = board.create('riemannsum',
2315  *               [[g,f], function(){return s.Value();}, 'lower', 0, 4],
2316  *               {fillOpacity:0.4}
2317  *               );
2318  *   var f = board.create('functiongraph',[f, -2, 5]);
2319  *   var g = board.create('functiongraph',[g, -2, 5]);
2320  *   var t = board.create('text',[-2,-2, function(){ return 'Sum=' + JXG.toFixed(r.Value(), 4); }]);
2321  * })();
2322  * </script><pre>
2323  */
2324 JXG.createRiemannsum = function (board, parents, attributes) {
2325     var n, type, f, par, c, attr;
2326 
2327     attr = Type.copyAttributes(attributes, board.options, "riemannsum");
2328     attr.curvetype = "plot";
2329 
2330     f = parents[0];
2331     n = Type.createFunction(parents[1], board, "");
2332 
2333     if (!Type.exists(n)) {
2334         throw new Error(
2335             "JSXGraph: JXG.createRiemannsum: argument '2' n has to be number or function." +
2336                 "\nPossible parent types: [function,n:number|function,type,start:number|function,end:number|function]"
2337         );
2338     }
2339 
2340     type = Type.createFunction(parents[2], board, "");
2341     if (!Type.exists(type)) {
2342         throw new Error(
2343             "JSXGraph: JXG.createRiemannsum: argument 3 'type' has to be string or function." +
2344                 "\nPossible parent types: [function,n:number|function,type,start:number|function,end:number|function]"
2345         );
2346     }
2347 
2348     par = [[0], [0]].concat(parents.slice(3));
2349 
2350     c = board.create("curve", par, attr);
2351 
2352     c.sum = 0.0;
2353     /**
2354      * Returns the value of the Riemann sum, i.e. the sum of the (signed) areas of the rectangles.
2355      * @name Value
2356      * @memberOf Riemannsum.prototype
2357      * @function
2358      * @returns {Number} value of Riemann sum.
2359      */
2360     c.Value = function () {
2361         return this.sum;
2362     };
2363 
2364     /**
2365      * @class
2366      * @ignore
2367      */
2368     c.updateDataArray = function () {
2369         var u = Numerics.riemann(f, n(), type(), this.minX(), this.maxX());
2370         this.dataX = u[0];
2371         this.dataY = u[1];
2372 
2373         // Update "Riemann sum"
2374         this.sum = u[2];
2375     };
2376 
2377     c.addParentsFromJCFunctions([n, type]);
2378 
2379     return c;
2380 };
2381 
2382 JXG.registerElement("riemannsum", JXG.createRiemannsum);
2383 
2384 /**
2385  * @class This element is used to provide a constructor for trace curve (simple locus curve), which is realized as a special curve.
2386  * @pseudo
2387  * @name Tracecurve
2388  * @augments JXG.Curve
2389  * @constructor
2390  * @type Object
2391  * @descript JXG.Curve
2392  * @param {Point} Parent elements of Tracecurve are a
2393  *         glider point and a point whose locus is traced.
2394  * @param {point}
2395  * @see JXG.Curve
2396  * @example
2397  * // Create trace curve.
2398  * var c1 = board.create('circle',[[0, 0], [2, 0]]),
2399  * p1 = board.create('point',[-3, 1]),
2400  * g1 = board.create('glider',[2, 1, c1]),
2401  * s1 = board.create('segment',[g1, p1]),
2402  * p2 = board.create('midpoint',[s1]),
2403  * curve = board.create('tracecurve', [g1, p2]);
2404  *
2405  * </pre><div class="jxgbox" id="JXG5749fb7d-04fc-44d2-973e-45c1951e29ad" style="width: 300px; height: 300px;"></div>
2406  * <script type="text/javascript">
2407  *   var tc1_board = JXG.JSXGraph.initBoard('JXG5749fb7d-04fc-44d2-973e-45c1951e29ad', {boundingbox: [-4, 4, 4, -4], axis: false, showcopyright: false, shownavigation: false});
2408  *   var c1 = tc1_board.create('circle',[[0, 0], [2, 0]]),
2409  *       p1 = tc1_board.create('point',[-3, 1]),
2410  *       g1 = tc1_board.create('glider',[2, 1, c1]),
2411  *       s1 = tc1_board.create('segment',[g1, p1]),
2412  *       p2 = tc1_board.create('midpoint',[s1]),
2413  *       curve = tc1_board.create('tracecurve', [g1, p2]);
2414  * </script><pre>
2415  */
2416 JXG.createTracecurve = function (board, parents, attributes) {
2417     var c, glider, tracepoint, attr;
2418 
2419     if (parents.length !== 2) {
2420         throw new Error(
2421             "JSXGraph: Can't create trace curve with given parent'" +
2422                 "\nPossible parent types: [glider, point]"
2423         );
2424     }
2425 
2426     glider = board.select(parents[0]);
2427     tracepoint = board.select(parents[1]);
2428 
2429     if (glider.type !== Const.OBJECT_TYPE_GLIDER || !Type.isPoint(tracepoint)) {
2430         throw new Error(
2431             "JSXGraph: Can't create trace curve with parent types '" +
2432                 typeof parents[0] +
2433                 "' and '" +
2434                 typeof parents[1] +
2435                 "'." +
2436                 "\nPossible parent types: [glider, point]"
2437         );
2438     }
2439 
2440     attr = Type.copyAttributes(attributes, board.options, "tracecurve");
2441     attr.curvetype = "plot";
2442     c = board.create("curve", [[0], [0]], attr);
2443 
2444     /**
2445      * @class
2446      * @ignore
2447      */
2448     c.updateDataArray = function () {
2449         var i, step, t, el, pEl, x, y, from,
2450             savetrace,
2451             le = attr.numberpoints,
2452             savePos = glider.position,
2453             slideObj = glider.slideObject,
2454             mi = slideObj.minX(),
2455             ma = slideObj.maxX();
2456 
2457         // set step width
2458         step = (ma - mi) / le;
2459         this.dataX = [];
2460         this.dataY = [];
2461 
2462         /*
2463          * For gliders on circles and lines a closed curve is computed.
2464          * For gliders on curves the curve is not closed.
2465          */
2466         if (slideObj.elementClass !== Const.OBJECT_CLASS_CURVE) {
2467             le++;
2468         }
2469 
2470         // Loop over all steps
2471         for (i = 0; i < le; i++) {
2472             t = mi + i * step;
2473             x = slideObj.X(t) / slideObj.Z(t);
2474             y = slideObj.Y(t) / slideObj.Z(t);
2475 
2476             // Position the glider
2477             glider.setPositionDirectly(Const.COORDS_BY_USER, [x, y]);
2478             from = false;
2479 
2480             // Update all elements from the glider up to the trace element
2481             for (el in this.board.objects) {
2482                 if (this.board.objects.hasOwnProperty(el)) {
2483                     pEl = this.board.objects[el];
2484 
2485                     if (pEl === glider) {
2486                         from = true;
2487                     }
2488 
2489                     if (from && pEl.needsRegularUpdate) {
2490                         // Save the trace mode of the element
2491                         savetrace = pEl.visProp.trace;
2492                         pEl.visProp.trace = false;
2493                         pEl.needsUpdate = true;
2494                         pEl.update(true);
2495 
2496                         // Restore the trace mode
2497                         pEl.visProp.trace = savetrace;
2498                         if (pEl === tracepoint) {
2499                             break;
2500                         }
2501                     }
2502                 }
2503             }
2504 
2505             // Store the position of the trace point
2506             this.dataX[i] = tracepoint.X();
2507             this.dataY[i] = tracepoint.Y();
2508         }
2509 
2510         // Restore the original position of the glider
2511         glider.position = savePos;
2512         from = false;
2513 
2514         // Update all elements from the glider to the trace point
2515         for (el in this.board.objects) {
2516             if (this.board.objects.hasOwnProperty(el)) {
2517                 pEl = this.board.objects[el];
2518                 if (pEl === glider) {
2519                     from = true;
2520                 }
2521 
2522                 if (from && pEl.needsRegularUpdate) {
2523                     savetrace = pEl.visProp.trace;
2524                     pEl.visProp.trace = false;
2525                     pEl.needsUpdate = true;
2526                     pEl.update(true);
2527                     pEl.visProp.trace = savetrace;
2528 
2529                     if (pEl === tracepoint) {
2530                         break;
2531                     }
2532                 }
2533             }
2534         }
2535     };
2536 
2537     return c;
2538 };
2539 
2540 JXG.registerElement("tracecurve", JXG.createTracecurve);
2541 
2542 /**
2543      * @class This element is used to provide a constructor for step function, which is realized as a special curve.
2544      *
2545      * In case the data points should be updated after creation time, they can be accessed by curve.xterm and curve.yterm.
2546      * @pseudo
2547      * @name Stepfunction
2548      * @augments JXG.Curve
2549      * @constructor
2550      * @type Curve
2551      * @description JXG.Curve
2552      * @param {Array|Function} Parent1 elements of Stepfunction are two arrays containing the coordinates.
2553      * @param {Array|Function} Parent2
2554      * @see JXG.Curve
2555      * @example
2556      * // Create step function.
2557      var curve = board.create('stepfunction', [[0,1,2,3,4,5], [1,3,0,2,2,1]]);
2558 
2559      * </pre><div class="jxgbox" id="JXG32342ec9-ad17-4339-8a97-ff23dc34f51a" style="width: 300px; height: 300px;"></div>
2560      * <script type="text/javascript">
2561      *   var sf1_board = JXG.JSXGraph.initBoard('JXG32342ec9-ad17-4339-8a97-ff23dc34f51a', {boundingbox: [-1, 5, 6, -2], axis: true, showcopyright: false, shownavigation: false});
2562      *   var curve = sf1_board.create('stepfunction', [[0,1,2,3,4,5], [1,3,0,2,2,1]]);
2563      * </script><pre>
2564      */
2565 JXG.createStepfunction = function (board, parents, attributes) {
2566     var c, attr;
2567     if (parents.length !== 2) {
2568         throw new Error(
2569             "JSXGraph: Can't create step function with given parent'" +
2570                 "\nPossible parent types: [array, array|function]"
2571         );
2572     }
2573 
2574     attr = Type.copyAttributes(attributes, board.options, "stepfunction");
2575     c = board.create("curve", parents, attr);
2576     /**
2577      * @class
2578      * @ignore
2579      */
2580     c.updateDataArray = function () {
2581         var i,
2582             j = 0,
2583             len = this.xterm.length;
2584 
2585         this.dataX = [];
2586         this.dataY = [];
2587 
2588         if (len === 0) {
2589             return;
2590         }
2591 
2592         this.dataX[j] = this.xterm[0];
2593         this.dataY[j] = this.yterm[0];
2594         ++j;
2595 
2596         for (i = 1; i < len; ++i) {
2597             this.dataX[j] = this.xterm[i];
2598             this.dataY[j] = this.dataY[j - 1];
2599             ++j;
2600             this.dataX[j] = this.xterm[i];
2601             this.dataY[j] = this.yterm[i];
2602             ++j;
2603         }
2604     };
2605 
2606     return c;
2607 };
2608 
2609 JXG.registerElement("stepfunction", JXG.createStepfunction);
2610 
2611 /**
2612  * @class This element is used to provide a constructor for the graph showing
2613  * the (numerical) derivative of a given curve.
2614  *
2615  * @pseudo
2616  * @name Derivative
2617  * @augments JXG.Curve
2618  * @constructor
2619  * @type JXG.Curve
2620  * @param {JXG.Curve} Parent Curve for which the derivative is generated.
2621  * @see JXG.Curve
2622  * @example
2623  * var cu = board.create('cardinalspline', [[[-3,0], [-1,2], [0,1], [2,0], [3,1]], 0.5, 'centripetal'], {createPoints: false});
2624  * var d = board.create('derivative', [cu], {dash: 2});
2625  *
2626  * </pre><div id="JXGb9600738-1656-11e8-8184-901b0e1b8723" class="jxgbox" style="width: 300px; height: 300px;"></div>
2627  * <script type="text/javascript">
2628  *     (function() {
2629  *         var board = JXG.JSXGraph.initBoard('JXGb9600738-1656-11e8-8184-901b0e1b8723',
2630  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
2631  *     var cu = board.create('cardinalspline', [[[-3,0], [-1,2], [0,1], [2,0], [3,1]], 0.5, 'centripetal'], {createPoints: false});
2632  *     var d = board.create('derivative', [cu], {dash: 2});
2633  *
2634  *     })();
2635  *
2636  * </script><pre>
2637  *
2638  */
2639 JXG.createDerivative = function (board, parents, attributes) {
2640     var c, curve, dx, dy, attr;
2641 
2642     if (parents.length !== 1 && parents[0].class !== Const.OBJECT_CLASS_CURVE) {
2643         throw new Error(
2644             "JSXGraph: Can't create derivative curve with given parent'" +
2645                 "\nPossible parent types: [curve]"
2646         );
2647     }
2648 
2649     attr = Type.copyAttributes(attributes, board.options, "curve");
2650 
2651     curve = parents[0];
2652     dx = Numerics.D(curve.X);
2653     dy = Numerics.D(curve.Y);
2654 
2655     c = board.create(
2656         "curve",
2657         [
2658             function (t) {
2659                 return curve.X(t);
2660             },
2661             function (t) {
2662                 return dy(t) / dx(t);
2663             },
2664             curve.minX(),
2665             curve.maxX()
2666         ],
2667         attr
2668     );
2669 
2670     c.setParents(curve);
2671 
2672     return c;
2673 };
2674 
2675 JXG.registerElement("derivative", JXG.createDerivative);
2676 
2677 /**
2678  * @class Intersection of two closed path elements. The elements may be of type curve, circle, polygon, inequality.
2679  * If one element is a curve, it has to be closed.
2680  * The resulting element is of type curve.
2681  * @pseudo
2682  * @name CurveIntersection
2683  * @param {JXG.Curve|JXG.Polygon|JXG.Circle} curve1 First element which is intersected
2684  * @param {JXG.Curve|JXG.Polygon|JXG.Circle} curve2 Second element which is intersected
2685  * @augments JXG.Curve
2686  * @constructor
2687  * @type JXG.Curve
2688  *
2689  * @example
2690  * var f = board.create('functiongraph', ['cos(x)']);
2691  * var ineq = board.create('inequality', [f], {inverse: true, fillOpacity: 0.1});
2692  * var circ = board.create('circle', [[0,0], 4]);
2693  * var clip = board.create('curveintersection', [ineq, circ], {fillColor: 'yellow', fillOpacity: 0.6});
2694  *
2695  * </pre><div id="JXGe2948257-8835-4276-9164-8acccb48e8d4" class="jxgbox" style="width: 300px; height: 300px;"></div>
2696  * <script type="text/javascript">
2697  *     (function() {
2698  *         var board = JXG.JSXGraph.initBoard('JXGe2948257-8835-4276-9164-8acccb48e8d4',
2699  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
2700  *     var f = board.create('functiongraph', ['cos(x)']);
2701  *     var ineq = board.create('inequality', [f], {inverse: true, fillOpacity: 0.1});
2702  *     var circ = board.create('circle', [[0,0], 4]);
2703  *     var clip = board.create('curveintersection', [ineq, circ], {fillColor: 'yellow', fillOpacity: 0.6});
2704  *
2705  *     })();
2706  *
2707  * </script><pre>
2708  *
2709  */
2710 JXG.createCurveIntersection = function (board, parents, attributes) {
2711     var c;
2712 
2713     if (parents.length !== 2) {
2714         throw new Error(
2715             "JSXGraph: Can't create curve intersection with given parent'" +
2716                 "\nPossible parent types: [array, array|function]"
2717         );
2718     }
2719 
2720     c = board.create("curve", [[], []], attributes);
2721     /**
2722      * @class
2723      * @ignore
2724      */
2725     c.updateDataArray = function () {
2726         var a = Clip.intersection(parents[0], parents[1], this.board);
2727         this.dataX = a[0];
2728         this.dataY = a[1];
2729     };
2730     return c;
2731 };
2732 
2733 /**
2734  * @class Union of two closed path elements. The elements may be of type curve, circle, polygon, inequality.
2735  * If one element is a curve, it has to be closed.
2736  * The resulting element is of type curve.
2737  * @pseudo
2738  * @name CurveUnion
2739  * @param {JXG.Curve|JXG.Polygon|JXG.Circle} curve1 First element defining the union
2740  * @param {JXG.Curve|JXG.Polygon|JXG.Circle} curve2 Second element defining the union
2741  * @augments JXG.Curve
2742  * @constructor
2743  * @type JXG.Curve
2744  *
2745  * @example
2746  * var f = board.create('functiongraph', ['cos(x)']);
2747  * var ineq = board.create('inequality', [f], {inverse: true, fillOpacity: 0.1});
2748  * var circ = board.create('circle', [[0,0], 4]);
2749  * var clip = board.create('curveunion', [ineq, circ], {fillColor: 'yellow', fillOpacity: 0.6});
2750  *
2751  * </pre><div id="JXGe2948257-8835-4276-9164-8acccb48e8d4" class="jxgbox" style="width: 300px; height: 300px;"></div>
2752  * <script type="text/javascript">
2753  *     (function() {
2754  *         var board = JXG.JSXGraph.initBoard('JXGe2948257-8835-4276-9164-8acccb48e8d4',
2755  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
2756  *     var f = board.create('functiongraph', ['cos(x)']);
2757  *     var ineq = board.create('inequality', [f], {inverse: true, fillOpacity: 0.1});
2758  *     var circ = board.create('circle', [[0,0], 4]);
2759  *     var clip = board.create('curveunion', [ineq, circ], {fillColor: 'yellow', fillOpacity: 0.6});
2760  *
2761  *     })();
2762  *
2763  * </script><pre>
2764  *
2765  */
2766 JXG.createCurveUnion = function (board, parents, attributes) {
2767     var c;
2768 
2769     if (parents.length !== 2) {
2770         throw new Error(
2771             "JSXGraph: Can't create curve union with given parent'" +
2772                 "\nPossible parent types: [array, array|function]"
2773         );
2774     }
2775 
2776     c = board.create("curve", [[], []], attributes);
2777     /**
2778      * @class
2779      * @ignore
2780      */
2781     c.updateDataArray = function () {
2782         var a = Clip.union(parents[0], parents[1], this.board);
2783         this.dataX = a[0];
2784         this.dataY = a[1];
2785     };
2786     return c;
2787 };
2788 
2789 /**
2790  * @class Difference of two closed path elements. The elements may be of type curve, circle, polygon, inequality.
2791  * If one element is a curve, it has to be closed.
2792  * The resulting element is of type curve.
2793  * @pseudo
2794  * @name CurveDifference
2795  * @param {JXG.Curve|JXG.Polygon|JXG.Circle} curve1 First element from which the second element is "subtracted"
2796  * @param {JXG.Curve|JXG.Polygon|JXG.Circle} curve2 Second element which is subtracted from the first element
2797  * @augments JXG.Curve
2798  * @constructor
2799  * @type JXG.Curve
2800  *
2801  * @example
2802  * var f = board.create('functiongraph', ['cos(x)']);
2803  * var ineq = board.create('inequality', [f], {inverse: true, fillOpacity: 0.1});
2804  * var circ = board.create('circle', [[0,0], 4]);
2805  * var clip = board.create('curvedifference', [ineq, circ], {fillColor: 'yellow', fillOpacity: 0.6});
2806  *
2807  * </pre><div id="JXGe2948257-8835-4276-9164-8acccb48e8d4" class="jxgbox" style="width: 300px; height: 300px;"></div>
2808  * <script type="text/javascript">
2809  *     (function() {
2810  *         var board = JXG.JSXGraph.initBoard('JXGe2948257-8835-4276-9164-8acccb48e8d4',
2811  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
2812  *     var f = board.create('functiongraph', ['cos(x)']);
2813  *     var ineq = board.create('inequality', [f], {inverse: true, fillOpacity: 0.1});
2814  *     var circ = board.create('circle', [[0,0], 4]);
2815  *     var clip = board.create('curvedifference', [ineq, circ], {fillColor: 'yellow', fillOpacity: 0.6});
2816  *
2817  *     })();
2818  *
2819  * </script><pre>
2820  *
2821  */
2822 JXG.createCurveDifference = function (board, parents, attributes) {
2823     var c;
2824 
2825     if (parents.length !== 2) {
2826         throw new Error(
2827             "JSXGraph: Can't create curve difference with given parent'" +
2828                 "\nPossible parent types: [array, array|function]"
2829         );
2830     }
2831 
2832     c = board.create("curve", [[], []], attributes);
2833     /**
2834      * @class
2835      * @ignore
2836      */
2837     c.updateDataArray = function () {
2838         var a = Clip.difference(parents[0], parents[1], this.board);
2839         this.dataX = a[0];
2840         this.dataY = a[1];
2841     };
2842     return c;
2843 };
2844 
2845 JXG.registerElement("curvedifference", JXG.createCurveDifference);
2846 JXG.registerElement("curveintersection", JXG.createCurveIntersection);
2847 JXG.registerElement("curveunion", JXG.createCurveUnion);
2848 
2849 // /**
2850 //  * @class Concat of two path elements, in general neither is a closed path. The parent elements have to be curves, too.
2851 //  * The resulting element is of type curve. The curve points are simply concatenated.
2852 //  * @pseudo
2853 //  * @name CurveConcat
2854 //  * @param {JXG.Curve} curve1 First curve element.
2855 //  * @param {JXG.Curve} curve2 Second curve element.
2856 //  * @augments JXG.Curve
2857 //  * @constructor
2858 //  * @type JXG.Curve
2859 //  */
2860 // JXG.createCurveConcat = function (board, parents, attributes) {
2861 //     var c;
2862 
2863 //     if (parents.length !== 2) {
2864 //         throw new Error(
2865 //             "JSXGraph: Can't create curve difference with given parent'" +
2866 //                 "\nPossible parent types: [array, array|function]"
2867 //         );
2868 //     }
2869 
2870 //     c = board.create("curve", [[], []], attributes);
2871 //     /**
2872 //      * @class
2873 //      * @ignore
2874 //      */
2875 //     c.updateCurve = function () {
2876 //         this.points = parents[0].points.concat(
2877 //                 [new JXG.Coords(Const.COORDS_BY_USER, [NaN, NaN], this.board)]
2878 //             ).concat(parents[1].points);
2879 //         this.numberPoints = this.points.length;
2880 //         return this;
2881 //     };
2882 
2883 //     return c;
2884 // };
2885 
2886 // JXG.registerElement("curveconcat", JXG.createCurveConcat);
2887 
2888 /**
2889  * @class Box plot curve. The direction of the box plot can be either vertical or horizontal which
2890  * is controlled by the attribute "dir".
2891  * @pseudo
2892  * @name Boxplot
2893  * @param {Array} quantiles Array containing at least five quantiles. The elements can be of type number, function or string.
2894  * @param {Number|Function} axis Axis position of the box plot
2895  * @param {Number|Function} width Width of the rectangle part of the box plot. The width of the first and 4th quantile
2896  * is relative to this width and can be controlled by the attribute "smallWidth".
2897  * @augments JXG.Curve
2898  * @constructor
2899  * @type JXG.Curve
2900  *
2901  * @example
2902  * var Q = [ -1, 2, 3, 3.5, 5 ];
2903  *
2904  * var b = board.create('boxplot', [Q, 2, 4], {strokeWidth: 3});
2905  *
2906  * </pre><div id="JXG13eb23a1-a641-41a2-be11-8e03e400a947" class="jxgbox" style="width: 300px; height: 300px;"></div>
2907  * <script type="text/javascript">
2908  *     (function() {
2909  *         var board = JXG.JSXGraph.initBoard('JXG13eb23a1-a641-41a2-be11-8e03e400a947',
2910  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
2911  *     var Q = [ -1, 2, 3, 3.5, 5 ];
2912  *     var b = board.create('boxplot', [Q, 2, 4], {strokeWidth: 3});
2913  *
2914  *     })();
2915  *
2916  * </script><pre>
2917  *
2918  * @example
2919  * var Q = [ -1, 2, 3, 3.5, 5 ];
2920  * var b = board.create('boxplot', [Q, 3, 4], {dir: 'horizontal', smallWidth: 0.25, color:'red'});
2921  *
2922  * </pre><div id="JXG0deb9cb2-84bc-470d-a6db-8be9a5694813" class="jxgbox" style="width: 300px; height: 300px;"></div>
2923  * <script type="text/javascript">
2924  *     (function() {
2925  *         var board = JXG.JSXGraph.initBoard('JXG0deb9cb2-84bc-470d-a6db-8be9a5694813',
2926  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
2927  *     var Q = [ -1, 2, 3, 3.5, 5 ];
2928  *     var b = board.create('boxplot', [Q, 3, 4], {dir: 'horizontal', smallWidth: 0.25, color:'red'});
2929  *
2930  *     })();
2931  *
2932  * </script><pre>
2933  *
2934  * @example
2935  * var data = [57, 57, 57, 58, 63, 66, 66, 67, 67, 68, 69, 70, 70, 70, 70, 72, 73, 75, 75, 76, 76, 78, 79, 81];
2936  * var Q = [];
2937  *
2938  * Q[0] = JXG.Math.Statistics.min(data);
2939  * Q = Q.concat(JXG.Math.Statistics.percentile(data, [25, 50, 75]));
2940  * Q[4] = JXG.Math.Statistics.max(data);
2941  *
2942  * var b = board.create('boxplot', [Q, 0, 3]);
2943  *
2944  * </pre><div id="JXGef079e76-ae99-41e4-af29-1d07d83bf85a" class="jxgbox" style="width: 300px; height: 300px;"></div>
2945  * <script type="text/javascript">
2946  *     (function() {
2947  *         var board = JXG.JSXGraph.initBoard('JXGef079e76-ae99-41e4-af29-1d07d83bf85a',
2948  *             {boundingbox: [-5,90,5,30], axis: true, showcopyright: false, shownavigation: false});
2949  *     var data = [57, 57, 57, 58, 63, 66, 66, 67, 67, 68, 69, 70, 70, 70, 70, 72, 73, 75, 75, 76, 76, 78, 79, 81];
2950  *     var Q = [];
2951  *
2952  *     Q[0] = JXG.Math.Statistics.min(data);
2953  *     Q = Q.concat(JXG.Math.Statistics.percentile(data, [25, 50, 75]));
2954  *     Q[4] = JXG.Math.Statistics.max(data);
2955  *
2956  *     var b = board.create('boxplot', [Q, 0, 3]);
2957  *
2958  *     })();
2959  *
2960  * </script><pre>
2961  *
2962  * @example
2963  * var mi = board.create('glider', [0, -1, board.defaultAxes.y]);
2964  * var ma = board.create('glider', [0, 5, board.defaultAxes.y]);
2965  * var Q = [function() { return mi.Y(); }, 2, 3, 3.5, function() { return ma.Y(); }];
2966  *
2967  * var b = board.create('boxplot', [Q, 0, 2]);
2968  *
2969  * </pre><div id="JXG3b3225da-52f0-42fe-8396-be9016bf289b" class="jxgbox" style="width: 300px; height: 300px;"></div>
2970  * <script type="text/javascript">
2971  *     (function() {
2972  *         var board = JXG.JSXGraph.initBoard('JXG3b3225da-52f0-42fe-8396-be9016bf289b',
2973  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
2974  *     var mi = board.create('glider', [0, -1, board.defaultAxes.y]);
2975  *     var ma = board.create('glider', [0, 5, board.defaultAxes.y]);
2976  *     var Q = [function() { return mi.Y(); }, 2, 3, 3.5, function() { return ma.Y(); }];
2977  *
2978  *     var b = board.create('boxplot', [Q, 0, 2]);
2979  *
2980  *     })();
2981  *
2982  * </script><pre>
2983  *
2984  */
2985 JXG.createBoxPlot = function (board, parents, attributes) {
2986     var box, i, len,
2987         attr = Type.copyAttributes(attributes, board.options, "boxplot");
2988 
2989     if (parents.length !== 3) {
2990         throw new Error(
2991             "JSXGraph: Can't create box plot with given parent'" +
2992                 "\nPossible parent types: [array, number|function, number|function] containing quantiles, axis, width"
2993         );
2994     }
2995     if (parents[0].length < 5) {
2996         throw new Error(
2997             "JSXGraph: Can't create box plot with given parent[0]'" +
2998                 "\nparent[0] has to contain at least 5 quantiles."
2999         );
3000     }
3001     box = board.create("curve", [[], []], attr);
3002 
3003     len = parents[0].length; // Quantiles
3004     box.Q = [];
3005     for (i = 0; i < len; i++) {
3006         box.Q[i] = Type.createFunction(parents[0][i], board);
3007     }
3008     box.x = Type.createFunction(parents[1], board);
3009     box.w = Type.createFunction(parents[2], board);
3010 
3011     /**
3012      * @class
3013      * @ignore
3014      */
3015     box.updateDataArray = function () {
3016         var v1, v2, l1, l2, r1, r2, w2, dir, x;
3017 
3018         w2 = Type.evaluate(this.visProp.smallwidth);
3019         dir = Type.evaluate(this.visProp.dir);
3020         x = this.x();
3021         l1 = x - this.w() * 0.5;
3022         l2 = x - this.w() * 0.5 * w2;
3023         r1 = x + this.w() * 0.5;
3024         r2 = x + this.w() * 0.5 * w2;
3025         v1 = [x, l2, r2, x, x, l1, l1, r1, r1, x, NaN, l1, r1, NaN, x, x, l2, r2, x];
3026         v2 = [
3027             this.Q[0](),
3028             this.Q[0](),
3029             this.Q[0](),
3030             this.Q[0](),
3031             this.Q[1](),
3032             this.Q[1](),
3033             this.Q[3](),
3034             this.Q[3](),
3035             this.Q[1](),
3036             this.Q[1](),
3037             NaN,
3038             this.Q[2](),
3039             this.Q[2](),
3040             NaN,
3041             this.Q[3](),
3042             this.Q[4](),
3043             this.Q[4](),
3044             this.Q[4](),
3045             this.Q[4]()
3046         ];
3047         if (dir === "vertical") {
3048             this.dataX = v1;
3049             this.dataY = v2;
3050         } else {
3051             this.dataX = v2;
3052             this.dataY = v1;
3053         }
3054     };
3055 
3056     box.addParentsFromJCFunctions([box.Q, box.x, box.w]);
3057 
3058     return box;
3059 };
3060 
3061 JXG.registerElement("boxplot", JXG.createBoxPlot);
3062 
3063 /**
3064  *
3065  * @class
3066  * From <a href="https://en.wikipedia.org/wiki/Implicit_curve">Wikipedia</a>:
3067  * "An implicit curve is a plane curve defined by an implicit equation
3068  * relating two coordinate variables, commonly <i>x</i> and <i>y</i>.
3069  * For example, the unit circle is defined by the implicit equation
3070  * x<sup>2</sup> + y<sup>2</sup> = 1.
3071  * In general, every implicit curve is defined by an equation of the form
3072  * <i>f(x, y) = 0</i>
3073  * for some function <i>f</i> of two variables."
3074  * <p>
3075  * The partial derivatives for <i>f</i> are optional. If not given, numerical
3076  * derivatives are used instead. This is good enough for most practical use cases.
3077  * But if supplied, both partial derivatives must be supplied.
3078  * <p>
3079  * The most effective attributes to tinker with if the implicit curve algorithm fails are
3080  * {@link ImplicitCurve#resolution_outer},
3081  * {@link ImplicitCurve#resolution_inner},
3082  * {@link ImplicitCurve#alpha_0},
3083  * {@link ImplicitCurve#h_initial},
3084  * {@link ImplicitCurve#h_max}, and
3085  * {@link ImplicitCurve#qdt_box}.
3086  *
3087  * @pseudo
3088  * @name ImplicitCurve
3089  * @param {Function|String} f Function of two variables for the left side of the equation <i>f(x,y)=0</i>.
3090  * If f is supplied as string, it has to use the variables 'x' and 'y'.
3091  * @param {Function|String} [dfx=null] Optional partial derivative in respect to the first variable
3092  * If dfx is supplied as string, it has to use the variables 'x' and 'y'.
3093  * @param {Function|String} [dfy=null] Optional partial derivative in respect to the second variable
3094  * If dfy is supplied as string, it has to use the variables 'x' and 'y'.
3095  * @augments JXG.Curve
3096  * @constructor
3097  * @type JXG.Curve
3098  *
3099  * @example
3100  *   var f, c;
3101  *   f = (x, y) => 1 / 16 * x ** 2 + y ** 2 - 1;
3102  *   c = board.create('implicitcurve', [f], {
3103  *       strokeWidth: 3,
3104  *       strokeColor: JXG.palette.red,
3105  *       strokeOpacity: 0.8
3106  *   });
3107  *
3108  * </pre><div id="JXGa6e86701-1a82-48d0-b007-3a3d32075076" class="jxgbox" style="width: 300px; height: 300px;"></div>
3109  * <script type="text/javascript">
3110  *     (function() {
3111  *         var board = JXG.JSXGraph.initBoard('JXGa6e86701-1a82-48d0-b007-3a3d32075076',
3112  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
3113  *             var f, c;
3114  *             f = (x, y) => 1 / 16 * x ** 2 + y ** 2 - 1;
3115  *             c = board.create('implicitcurve', [f], {
3116  *                 strokeWidth: 3,
3117  *                 strokeColor: JXG.palette.red,
3118  *                 strokeOpacity: 0.8
3119  *             });
3120  *
3121  *     })();
3122  *
3123  * </script><pre>
3124  *
3125  * @example
3126  *  var a, c, f;
3127  *  a = board.create('slider', [[-3, 6], [3, 6], [-3, 1, 3]], {
3128  *      name: 'a', stepWidth: 0.1
3129  *  });
3130  *  f = (x, y) => x ** 2 - 2 * x * y - 2 * x + (a.Value() + 1) * y ** 2 + (4 * a.Value() + 2) * y + 4 * a.Value() - 3;
3131  *  c = board.create('implicitcurve', [f], {
3132  *      strokeWidth: 3,
3133  *      strokeColor: JXG.palette.red,
3134  *      strokeOpacity: 0.8,
3135  *      resolution_outer: 20,
3136  *      resolution_inner: 20
3137  *  });
3138  *
3139  * </pre><div id="JXG0b133a54-9509-4a65-9722-9c5145e23b40" class="jxgbox" style="width: 300px; height: 300px;"></div>
3140  * <script type="text/javascript">
3141  *     (function() {
3142  *         var board = JXG.JSXGraph.initBoard('JXG0b133a54-9509-4a65-9722-9c5145e23b40',
3143  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
3144  *             var a, c, f;
3145  *             a = board.create('slider', [[-3, 6], [3, 6], [-3, 1, 3]], {
3146  *                 name: 'a', stepWidth: 0.1
3147  *             });
3148  *             f = (x, y) => x ** 2 - 2 * x * y - 2 * x + (a.Value() + 1) * y ** 2 + (4 * a.Value() + 2) * y + 4 * a.Value() - 3;
3149  *             c = board.create('implicitcurve', [f], {
3150  *                 strokeWidth: 3,
3151  *                 strokeColor: JXG.palette.red,
3152  *                 strokeOpacity: 0.8,
3153  *                 resolution_outer: 20,
3154  *                 resolution_inner: 20
3155  *             });
3156  *
3157  *     })();
3158  *
3159  * </script><pre>
3160  *
3161  * @example
3162  *  var c = board.create('implicitcurve', ['abs(x * y) - 3'], {
3163  *      strokeWidth: 3,
3164  *      strokeColor: JXG.palette.red,
3165  *      strokeOpacity: 0.8
3166  *  });
3167  *
3168  * </pre><div id="JXG02802981-0abb-446b-86ea-ee588f02ed1a" class="jxgbox" style="width: 300px; height: 300px;"></div>
3169  * <script type="text/javascript">
3170  *     (function() {
3171  *         var board = JXG.JSXGraph.initBoard('JXG02802981-0abb-446b-86ea-ee588f02ed1a',
3172  *             {boundingbox: [-8, 8, 8,-8], axis: true, showcopyright: false, shownavigation: false});
3173  *             var c = board.create('implicitcurve', ['abs(x * y) - 3'], {
3174  *                 strokeWidth: 3,
3175  *                 strokeColor: JXG.palette.red,
3176  *                 strokeOpacity: 0.8
3177  *             });
3178  *
3179  *     })();
3180  *
3181  * </script><pre>
3182  *
3183  */
3184 JXG.createImplicitCurve = function(board, parents, attributes) {
3185     var c, attr;
3186     if (parents.length !== 1 && parents.length !== 3) {
3187         throw new Error(
3188             "JSXGraph: Can't create curve implicitCurve with given parent'" +
3189                 "\nPossible parent types: [f] or [f, dfx, dfy]" +
3190                 "\nwith functions f, dfx, dfy"
3191         );
3192     }
3193 
3194     attr = Type.copyAttributes(attributes, board.options, "implicitcurve");
3195     c = board.create("curve", [[], []], attr);
3196 
3197     /**
3198      * Function of two variables for the left side of the equation <i>f(x,y)=0</i>.
3199      *
3200      * @name f
3201      * @memberOf ImplicitCurve.prototype
3202      * @function
3203      * @returns {Number}
3204      */
3205     c.f = Type.createFunction(parents[0], board, 'x, y');
3206 
3207     /**
3208      * Partial derivative in the first variable of
3209      * the left side of the equation <i>f(x,y)=0</i>.
3210      * If null, then numerical derivative is used.
3211      *
3212      * @name dfx
3213      * @memberOf ImplicitCurve.prototype
3214      * @function
3215      * @returns {Number}
3216      */
3217     c.dfx = Type.createFunction(parents[1], board, 'x, y');
3218 
3219     /**
3220      * Partial derivative in the second variable of
3221      * the left side of the equation <i>f(x,y)=0</i>.
3222      * If null, then numerical derivative is used.
3223      *
3224      * @name dfy
3225      * @memberOf ImplicitCurve.prototype
3226      * @function
3227      * @returns {Number}
3228      */
3229     c.dfy = Type.createFunction(parents[2], board, 'x, y');
3230 
3231     /**
3232      * @class
3233      * @ignore
3234      */
3235     c.updateDataArray = function () {
3236         var bbox = this.board.getBoundingBox(),
3237             ip, cfg,
3238             ret = [],
3239             mgn = Type.evaluate(this.visProp.margin);
3240 
3241         bbox[0] -= mgn;
3242         bbox[1] += mgn;
3243         bbox[2] += mgn;
3244         bbox[3] -= mgn;
3245 
3246         cfg = {
3247             resolution_out: Math.max(0.01, Type.evaluate(this.visProp.resolution_outer)),
3248             resolution_in: Math.max(0.01, Type.evaluate(this.visProp.resolution_inner)),
3249             max_steps: Type.evaluate(this.visProp.max_steps),
3250             alpha_0: Type.evaluate(this.visProp.alpha_0),
3251             tol_u0: Type.evaluate(this.visProp.tol_u0),
3252             tol_newton: Type.evaluate(this.visProp.tol_newton),
3253             tol_cusp: Type.evaluate(this.visProp.tol_cusp),
3254             tol_progress: Type.evaluate(this.visProp.tol_progress),
3255             qdt_box: Type.evaluate(this.visProp.qdt_box),
3256             kappa_0: Type.evaluate(this.visProp.kappa_0),
3257             delta_0: Type.evaluate(this.visProp.delta_0),
3258             h_initial: Type.evaluate(this.visProp.h_initial),
3259             h_critical: Type.evaluate(this.visProp.h_critical),
3260             h_max: Type.evaluate(this.visProp.h_max),
3261             loop_dist: Type.evaluate(this.visProp.loop_dist),
3262             loop_dir: Type.evaluate(this.visProp.loop_dir),
3263             loop_detection: Type.evaluate(this.visProp.loop_detection),
3264             unitX: this.board.unitX,
3265             unitY: this.board.unitY
3266         };
3267         this.dataX = [];
3268         this.dataY = [];
3269 
3270         // console.time("implicit plot");
3271         ip = new ImplicitPlot(bbox, cfg, this.f, this.dfx, this.dfy);
3272         this.qdt = ip.qdt;
3273 
3274         ret = ip.plot();
3275         // console.timeEnd("implicit plot");
3276 
3277         this.dataX = ret[0];
3278         this.dataY = ret[1];
3279     };
3280 
3281     c.elType = 'implicitcurve';
3282 
3283     return c;
3284 };
3285 
3286 JXG.registerElement("implicitcurve", JXG.createImplicitCurve);
3287 
3288 
3289 export default JXG.Curve;
3290 
3291 // export default {
3292 //     Curve: JXG.Curve,
3293 //     createCardinalSpline: JXG.createCardinalSpline,
3294 //     createCurve: JXG.createCurve,
3295 //     createCurveDifference: JXG.createCurveDifference,
3296 //     createCurveIntersection: JXG.createCurveIntersection,
3297 //     createCurveUnion: JXG.createCurveUnion,
3298 //     createDerivative: JXG.createDerivative,
3299 //     createFunctiongraph: JXG.createFunctiongraph,
3300 //     createMetapostSpline: JXG.createMetapostSpline,
3301 //     createPlot: JXG.createFunctiongraph,
3302 //     createSpline: JXG.createSpline,
3303 //     createRiemannsum: JXG.createRiemannsum,
3304 //     createStepfunction: JXG.createStepfunction,
3305 //     createTracecurve: JXG.createTracecurve
3306 // };
3307 
3308 // const Curve = JXG.Curve;
3309 // export { Curve as default, Curve};
3310