How to Incorporate a Numerical Solution into a Physics Java Applet?

[Robben]

Homework Statement

[/B]
I would like to make a physics applet.

I have a numerical solution of the Lotka-Volterra model located here:
https://www.physicsforums.com/threads/lotka-volterra-model-eulers-method.803382/#post-5044961

Homework Equations

None

The Attempt at a Solution

[/B]
I want to be able to make graphs of my numerical solution and I am wondering how do I incorporate my numerical solution of the Lotka-Volterra model into an applet?

I tried searching GUI applets for Java but it is so broad the I would like to narrow it down for only physics application like making graphs or making a wave that corresponds to the wave equation.

Any links or videos of how to make a physics applet would be of great help.

My numerical solution:

public class Lotka {
    public static void main(String[] args) {
        double[] prey = new double[1000];
        double[] predator = new double[1000];
        double[] dt = new double[101];
        double[] b = new double[101];
        prey[0] = 10;
        predator[0] = 5;   
        dt[0] = 0;
        b[0] = 0.01;   
   
        for (int j = 1; j < 101; j ++) {
            dt[j] = 2 + dt[j-1];
            b[j] = b[0]*((double)j/2);  
        }    
   
        for(int i = 1; i < 100; i++) {
            prey[i] = prey[i-1] + (0.2*prey[i-1]*(1-prey[i-1]/500)
               -(b[i]*prey[i-1]*predator[i-1])/(1+b[i]*prey[i-1]))*(1/dt[i]);
            predator[i] = predator[i-1] + (0.1*predator[i-1]*(1-predator[i-1]
                /(0.2*prey[i-1])))*(1/dt[i]);
            //System.out.println("" + prey[i] + " " + predator[i]);  
        }      
    }      
}

 

[jedishrfu]

Checkout Open Source Physics at www.compadre.org/osp

They have a whole collection of java software for making physics simulations including charting and ODE solvers.

 

[Robben]

Checkout Open Source Physics at www.compadre.org/osp

They have a whole collection of java software for making physics simulations including charting and ODE solvers.

Thanks for the link! I will be studying it now.

 

[Robben]

Checkout Open Source Physics at www.compadre.org/osp

They have a whole collection of java software for making physics simulations including charting and ODE solvers.

I noticed, in order to draw a line in my java applet it must be integers, i.e. for Graphics g then g.drawLine() must have int values and not double. Since my Lotka model numerical solution has double values from 10.0 to 9.87 (for the prey) and 4.99 to 4.82 (for the predator) how do I go about doing this? How do I get my drawline to take in double values instead of int?

 

[jedishrfu]

you have to develop scaling for what you want to draw

So say you decide your image is 1000x1000 pixels and your measurements range from 0cm to 15cm then
to draw a 3cm line you must compute linelength = 3 * 1000 / 15 = 200 pixels...

 

[Robben]

[/code][/QUOTE]

you have to develop scaling for what you want to draw

So say you decide your image is 1000x1000 pixels and your measurements range from 0cm to 15cm then
to draw a 3cm line you must compute linelength = 3 * 1000 / 15 = 200 pixels...

Hm, my measurements are

$p_0 = 10, \ q _0 = 5$
$p_1 = 9.946, \ q_1 = 4.925$
$p_2 = 9.89538, \ q_2 = 4.85231$
$p_3 = 9.84803, \ q_3 = 4.78187$
$\ldots$ up to $4.99$ for predator (q) and $10.0$ for prey (p). Now my image pixel size is arbitrary and I just extended Applet, i.e. I have the following code in my applet:

import java.applet.*;
import java.awt.*;
import java.awt.event.*;

   public class LotkaApplet extends Applet
   implements MouseListener, ActionListener, Runnable{
...
}

 

[jedishrfu]

Use getWidth() and getHeight() java applet methods to get the canvas size .

 

[Robben]

Use getWidth() and getHeight() java applet methods to get the canvas size .

I think I would have to extend 2D graphics for this.

 

[jedishrfu]

Its part of the Aplet class so you can either use getWidth() or this.getWidth().

Examples are easily googleable:

http://chortle.ccsu.edu/java5/Notes/chap36\ch36_16.html