Difference between revisions of "Logistic process"

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Line 20: Line 20:
 
var s = brd.createElement('slider', [[0,-5], [10,-5],[-5,0.5,5]], {name:'s'});
 
var s = brd.createElement('slider', [[0,-5], [10,-5],[-5,0.5,5]], {name:'s'});
 
var alpha = brd.createElement('slider', [[0,-6], [10,-6],[-1,0.2,2]], {name:'α'});
 
var alpha = brd.createElement('slider', [[0,-6], [10,-6],[-1,0.2,2]], {name:'α'});
//var e = brd.createElement('functiongraph', [function(x){return s.X()*Math.exp(alpha.X()*x);}],{strokeColor:'red'});
+
//var e = brd.createElement('functiongraph', [function(x){return s.Value()*Math.exp(alpha.Value()*x);}],{strokeColor:'red'});
  
 
t.hideTurtle();
 
t.hideTurtle();
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function run() {
 
function run() {
   t.setPos(0,s.X());
+
   t.setPos(0,s.Value());
 
   t.setPenSize(4);
 
   t.setPenSize(4);
   delta = 0.1; // global
+
   dx = 0.1; // global
 
   x = 0.0;  // global
 
   x = 0.0;  // global
 
   loop();
 
   loop();
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function loop() {
 
function loop() {
   var y = (alpha.X()*t.pos[1]-tau*t.pos[1]*t.pos[1])*delta; // Logistic process
+
   var dy = (alpha.Value()*t.Y()-tau*t.Y()*t.Y())*dx; // Logistic process
   t.moveTo([delta+t.pos[0],y+t.pos[1]]);
+
   t.moveTo([dx+t.X(),dy+t.Y());
   x += delta;
+
   x += dx;
 
   if (x<20.0) {
 
   if (x<20.0) {
 
     setTimeout(loop,10);
 
     setTimeout(loop,10);

Revision as of 08:46, 23 June 2009

Logistic population growth model

In time [math] \Delta t[/math] the population grows by [math]\alpha\cdot y -\tau\cdot y^2[/math] elements: [math] \Delta y = (\alpha\cdot y- \tau\cdot y^2)\cdot \Delta t[/math], that is [math] \frac{\Delta y}{\Delta t} = \alpha\cdot y -\tau\cdot y^2[/math].

With [math]\Delta t\to 0[/math] we get [math] \frac{d y}{d t} = \alpha\cdot y -\tau\cdot y^2 [/math], i.e. [math] y' = \alpha\cdot y -\tau\cdot y^2 [/math].

The initial population is [math]y(0)= s[/math], [math]\tau:=0.3[/math].

The blue line is the simulation with [math]\Delta t = 0.1[/math].

Other models

The JavaScript code

<jsxgraph height="500" width="600" board="board"  box="box1">
brd = JXG.JSXGraph.initBoard('box1', {originX: 10, originY: 250, unitX: 40, unitY: 20, axis:true});
var t = brd.createElement('turtle',[4,3,70]);
            
var s = brd.createElement('slider', [[0,-5], [10,-5],[-5,0.5,5]], {name:'s'});
var alpha = brd.createElement('slider', [[0,-6], [10,-6],[-1,0.2,2]], {name:'&alpha;'});
var e = brd.createElement('functiongraph', [function(x){return s.X()*Math.exp(alpha.X()*x);}],{strokeColor:'red'});

t.hideTurtle();

tau = 0.3;           
function clearturtle() {
  t.cs();
  t.ht();
}
            
function run() {
  t.setPos(0,s.X());
  t.setPenSize(4);
  delta = 0.1; // global
  x = 0.0;  // global
  loop();
}
             
function loop() {
  var y = (alpha.X()*t.pos[1]-tau*t.pos[1]*t.pos[1])*delta; // Logistic process
  t.moveTo([delta+t.pos[0],y+t.pos[1]]);
  x += delta;
  if (x<20.0) {
     setTimeout(loop,10);
  }
}
</jsxgraph>