Difference between revisions of "Change Equation of a Graph"

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'''Create a JavaScript Function f(x) From the Text Field'''
 
'''Create a JavaScript Function f(x) From the Text Field'''
 
<source lang="javascript">
 
<source lang="javascript">
  eval("function f(x){ return "+document.getElementById("eingabe").value+";}");
+
eval("function f(x){ return "+document.getElementById("eingabe").value+";}");
 
</source>
 
</source>
  
 
'''Use f(x) for defining the Graph'''
 
'''Use f(x) for defining the Graph'''
 
<source lang="javascript">
 
<source lang="javascript">
  graph = board.createElement('curve', [function(x){ return x; }, function(x){ return f(x); }, "x", -10, 10]);
+
graph = board.createElement('curve', [function(x){ return x; }, function(x){ return f(x); }, "x", -10, 10]);
 
</source>
 
</source>
  
 
'''Define Further Elements'''
 
'''Define Further Elements'''
 
<source lang="javascript">
 
<source lang="javascript">
  //glider on the curve
+
//glider on the curve
  p1 = board.createElement('glider', [graph], {style:6, name:'P'});
+
p1 = board.createElement('glider', [graph], {style:6, name:'P'});
  //define the derivative of f
+
//define the derivative of f
  g = board.algebra.D(f);
+
g = board.algebra.D(f);
  //a point on the tangent
+
//a point on the tangent
  //                                variable x coordinate          variable y coordinate depending on the derivative of f at point p1.X()
+
//                                variable x coordinate          variable y coordinate depending on the derivative of f at point p1.X()
  p2 = board.createElement('point', [function() { return p1.X()+1;}, function() {return p1.Y()+board.algebra.D(graph.Y)(p1.X());}], {style:1, name:''});
+
p2 = board.createElement('point', [function() { return p1.X()+1;}, function() {return p1.Y()+board.algebra.D(graph.Y)(p1.X());}], {style:1, name:''});
  //the tangent  
+
//the tangent  
  l1 = board.createElement('line', [p1,p2],{});  
+
l1 = board.createElement('line', [p1,p2],{});  
  //a third point fpr the slope triangle
+
//a third point fpr the slope triangle
  p3 = board.createElement('point', [function() { return p2.X();}, function() {return p1.Y();}],{style:1, name:''});
+
p3 = board.createElement('point', [function() { return p2.X();}, function() {return p1.Y();}],{style:1, name:''});
  //the slope triangle
+
//the slope triangle
  pol = board.createElement('polygon', [p1,p2,p3], {});
+
pol = board.createElement('polygon', [p1,p2,p3], {});
  //a text for displaying slope's value
+
//a text for displaying slope's value
  //                              variable x coordinate          variable y coordinate                        variable value
+
//                              variable x coordinate          variable y coordinate                        variable value
  t = board.createElement('text', [function(){return p1.X()+1.1;},function(){return p1.Y()+(p2.Y()-p3.Y())/2;},function(){ return "m="+(board.round(p2.Y()-p3.Y(),2));}],{color:ff0000});  
+
t = board.createElement('text', [function(){return p1.X()+1.1;},function(){return p1.Y()+(p2.Y()-p3.Y())/2;},function(){ return "m="+(board.round(p2.Y()-p3.Y(),2));}],{color:ff0000});  
 
</source>
 
</source>
  
 
'''Define JavaScript Function doIt() for Reacting on User Input'''
 
'''Define JavaScript Function doIt() for Reacting on User Input'''
 
<source lang="javascript">
 
<source lang="javascript">
  function doIt(){
+
function doIt(){
    //redefine function f according to the current text field value
+
//redefine function f according to the current text field value
    eval("function f(x){ return "+document.getElementById("eingabe").value+";}");
+
eval("function f(x){ return "+document.getElementById("eingabe").value+";}");
    //change the yterm attribute of the graph to the new function  
+
//change the yterm attribute of the graph to the new function  
    graph.yterm = function(x){ return f(x); };
+
graph.yterm = function(x){ return f(x); };
    graph.Y = graph.yterm;
+
graph.Y = graph.yterm;
    //update the graph
+
//update the graph
    graph.updateCurve();
+
graph.updateCurve();
    //update the whole board
+
//update the whole board
    board.update();
+
board.update();
  }  
+
}  
 
</source>
 
</source>
  
 
== Remarks ==
 
== Remarks ==
 
The doIt() function is only responsible for updating the graph. All other dependend objects are self-updating, especially the object p2 which depends on the derivative of function f. This is all done by aononymous functions of JavaScript.
 
The doIt() function is only responsible for updating the graph. All other dependend objects are self-updating, especially the object p2 which depends on the derivative of function f. This is all done by aononymous functions of JavaScript.

Revision as of 15:06, 15 September 2008

This example shows how you can change the equation of a graph without creating the whole construction again.



How to Create this Construction

HTML Part

Adding a text input field somewhere on the page together with a button

<input type="text" id="eingabe" value="Math.sin(x)*Math.cos(x)">
<input type="button" value="set" onClick="doIt()">

JavaScript Part

Setting up the board

board = JXG.JSXGraph.initBoard('jxgbox', {originX: 250, originY: 250, unitX: 40, unitY: 20});
// Axes
b1axisx = board.createElement('axis', [[1,0], [0,0]], {});
b1axisy = board.createElement('axis', [[0,1], [0,0]], {});

Create a JavaScript Function f(x) From the Text Field

eval("function f(x){ return "+document.getElementById("eingabe").value+";}");

Use f(x) for defining the Graph

graph = board.createElement('curve', [function(x){ return x; }, function(x){ return f(x); }, "x", -10, 10]);

Define Further Elements

//glider on the curve
p1 = board.createElement('glider', [graph], {style:6, name:'P'});
//define the derivative of f
g = board.algebra.D(f);
//a point on the tangent
//                                 variable x coordinate           variable y coordinate depending on the derivative of f at point p1.X()
p2 = board.createElement('point', [function() { return p1.X()+1;}, function() {return p1.Y()+board.algebra.D(graph.Y)(p1.X());}], {style:1, name:''});
//the tangent 
l1 = board.createElement('line', [p1,p2],{}); 
//a third point fpr the slope triangle
p3 = board.createElement('point', [function() { return p2.X();}, function() {return p1.Y();}],{style:1, name:''});
//the slope triangle
pol = board.createElement('polygon', [p1,p2,p3], {});
//a text for displaying slope's value
//                               variable x coordinate          variable y coordinate                        variable value
t = board.createElement('text', [function(){return p1.X()+1.1;},function(){return p1.Y()+(p2.Y()-p3.Y())/2;},function(){ return "m="+(board.round(p2.Y()-p3.Y(),2));}],{color:ff0000});

Define JavaScript Function doIt() for Reacting on User Input

function doIt(){
//redefine function f according to the current text field value
eval("function f(x){ return "+document.getElementById("eingabe").value+";}");
//change the yterm attribute of the graph to the new function 
graph.yterm = function(x){ return f(x); };
graph.Y = graph.yterm;
//update the graph
graph.updateCurve();
//update the whole board
board.update();
}

Remarks

The doIt() function is only responsible for updating the graph. All other dependend objects are self-updating, especially the object p2 which depends on the derivative of function f. This is all done by aononymous functions of JavaScript.