// $AISD_VERSION:RKDemo.java@1.2/home/coei/arc/archive%shell3.ba.best.com$

//COPYRIGHT: Copyright (c) 1997 by Christopher K. Oei, Incorporated.
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//COPYRIGHT: Permission to use, display, and modify this code
//COPYRIGHT: is hereby granted provided that:
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//COPYRIGHT: 1) this notice is included in its entirety
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// RKDemo is a class that demonstrates the use of the RKInt class
// by integrating an ODE of the form
//
// dx[0]/dt = -x[1] - 0.05 x[0]
// dx[1]/dt = x[0]
//


import RKInt;
import Potential;

public class RKDemo extends RKInt
{

public RKDemo(double i_t,double[] i_x,double i_dt)
    {
	super(i_t,i_x,i_dt);
    }

protected double[] derivative(double i_t,double[] i_x)
    {
	double q1 = Potential.q1;  
	double q2 = Potential.q2;  
	double q3 = Potential.q3;  
	double x2 = Potential.x2;  
	double y2 = Potential.y2;  
	double x3 = Potential.x3;  
	double y3 = Potential.y3;  
        double dist2;
        double dist3;
        double consta=1000000.;

	double compx;
	double compy;

	double[] y = new double[4];
	y[0]=i_x[2];
	y[1]=i_x[3];

        dist2 = Math.sqrt(Math.pow(i_x[0]-x2, 2) + Math.pow(i_x[1]-y2, 2));
        dist3 = Math.sqrt(Math.pow(i_x[0]-x3, 2) + Math.pow(i_x[1]-y3, 2));

        compx = q2*(i_x[0] - x2) / Math.pow(dist2,3) + q3* (i_x[0] - x3) / Math.pow(dist3,3);
             compy = q2*(i_x[1] - y2) / Math.pow(dist2,3) + q3*(i_x[1]-y3)/Math.pow(dist3,3);

//  restrict to one dimensional motion 
        y[2]= consta * q1 * compx;
	y[3]= consta * q1 * compy;
//      System.out.println("y[0]="+y[0] + " y[1]="+y[1] + " y[2]="+y[2] + " y[3]="+y[3]);
//      System.out.println("compx "+ compx + " compy "+ compy);
        return y;
    }
}