Remove a dif by zero in parabola.

jsxgraph · Feb 4, 2013 · e6c714a · e6c714a
1 parent c3a4fa3
commit e6c714a
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Showing 2 changed files with 10 additions and 7 deletions.
diff --git a/examples/construct.html b/examples/construct.html
@@ -56,8 +56,8 @@
     };
 
 
-    var brd = JXG.JSXGraph.initBoard('jxgbox',{boundingbox: [-1,5,5,-1], axis:true});
-    
+    var brd = JXG.JSXGraph.initBoard('jxgbox',{boundingbox: [-4,5,5,-4], axis:true});
+
     // Create two arcs
     //var l = brd.create('line', [-1,1,0]);
 /*
@@ -92,14 +92,15 @@
         }
         );
 */        
-
+/*
     var p1 = brd.create('point', [3,2], {withLabel:true, name:'FREEZE', frozen:false, visible:true});
     var p2 = brd.create('point', [3,1], {snapToPoints: false, visible:true});
     var s1 = brd.create('slider', [[1,3],[4,3],[10,40,110]], 
         {   point1:{frozen:true}, 
             point2:{frozen:true},
             ticks:{drawLabels:true}
         });
+*/        
 //brd.create('segment', [p1,p2], {strokeWidth:20, highlightStrokeWidth:2, firstArrow:true, lastArrow:true});
 /*
     var t1 = brd.create('text', [1,2,'hello'], {snapToGrid:true});
@@ -141,7 +142,7 @@
     brd.update();
 */
 
-    var tape = brd.create('tapemeasure', [[1,4],[3,4]], {name: 'd'});
+    //var tape = brd.create('tapemeasure', [[1,4],[3,4]], {name: 'd'});
 </script> 
 </body>
 </html>
diff --git a/src/element/conic.js b/src/element/conic.js
@@ -571,6 +571,7 @@
 
         polarForm = function (t, suspendUpdate) {
             var e = M.Dist(F1) * 0.5,
+                e4 = e * 4,
                 transformMat = [
                     [1, 0, 0],
                     [0, 1, 0],
@@ -593,13 +594,14 @@
                 curve.quadraticform =
                     JXG.Math.matMatMult(JXG.Math.transpose(transformMat),
                         JXG.Math.matMatMult([
-                            [-b * 4 * e - a * a, a, 2 * e],
+                            [-b * e4 - a * a, a, 2 * e],
                             [a, -1, 0],
                             [2 * e, 0, 0]
                         ], transformMat));
             }
-            return JXG.Math.matVecMult(rotationMatrix, [1, t + a, t * t / (e * 4) + b]);
+            return JXG.Math.matVecMult(rotationMatrix, [e4, e4 * (t + a), t * t + b * e4]);
         };
+
         curve.X = function (phi, suspendUpdate) {
             return polarForm(phi, suspendUpdate)[1];
         };
@@ -914,4 +916,4 @@
     JXG.JSXGraph.registerElement('hyperbola', JXG.createHyperbola);
     JXG.JSXGraph.registerElement('parabola', JXG.createParabola);
     JXG.JSXGraph.registerElement('conic', JXG.createConic);
-}());
+}());