Matrix multiplication II

The underlying JavaScript code

  var b1 = JXG.JSXGraph.initBoard('jxgbox', {boundingbox:[-10,10,10,-10], axis:true});
  b1.suspendUpdate();
  var a = b1.create('slider',[[-5,-2],[5,-2],[-5,1,5]],{name:'a', snapWidth:0.1});
  var b = b1.create('slider',[[-5,-3],[5,-3],[-5,0,5]],{name:'b', snapWidth:0.1});
  var c = b1.create('slider',[[-5,-4],[5,-4],[-5,0,5]],{name:'c', snapWidth:0.1});
  var d = b1.create('slider',[[-5,-5],[5,-5],[-5,1,5]],{name:'d', snapWidth:0.1});

  var v = b1.create('point',[2,2],{style:5,name:'v'});
  var va = b1.create('arrow',[[0,0],v]);

  var v2 = b1.create('point',[
       function() {return a.Value()*v.X()+b.Value()*v.Y();},
       function() {return c.Value()*v.X()+d.Value()*v.Y();}],{style:7,name:"v'"});
  var va2 = b1.create('arrow',[[0,0],v2],{color:'black', strokeWidth:1});

  var t = b1.create('text',[-8, 5, 
            function(){ return 'Matrix=<br>|' 
                        + b1.round(a.Value(),2) + ' '
                        + b1.round(b.Value(),2) + '|<br>|'
                        + b1.round(c.Value(),2) +' ' 
                        + b1.round(d.Value(),2)+'|';}]);

  var t2 = b1.create('text',[-8,1,
               function(){ return "&lambda; = |v'|/|v| = " 
                 + b1.round(
                     JXG.Math.Geometry.distance([0,0],[v2.X(),v2.Y()])/
                     JXG.Math.Geometry.distance([0,0],[v.X(),v.Y()]), 3
                   );}]);
  b1.unsuspendUpdate();