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

//COPYRIGHT: Copyright (c) 1997 by Christopher K. Oei, Incorporated.
//COPYRIGHT: 
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//COPYRIGHT: 
//COPYRIGHT: Permission to use, display, and modify this code
//COPYRIGHT: is hereby granted provided that:
//COPYRIGHT: 
//COPYRIGHT: 1) this notice is included in its entirety
//COPYRIGHT: 2) we are notified of the usage

// 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 NumDemo;

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 q = lev_mag.qvalue;  
	double beta = lev_mag.betavalue;
	double yst = lev_mag.ystat;
	int sign = lev_mag.sig;
	double yst1;
	double yst2 = 120.;

	double[] y = new double[3];
        yst1=30.+70.*(3.-i_x[0]);
        y[0]=i_x[2];
        y[1]=0.;
        if( yst1 > yst - 30. && sign > 0)
               {
                y[2] = 0.;
                y[0] = 0.;
               }
        else
               {
         	y[2]=-1.-((double)sign)*6.*Math.pow(yst2,4)/Math.pow(Math.pow(yst-yst1,2)+Math.pow(yst2,2),2.0)-q*i_x[2]/10.;
               }
//    System.out.println("x1= " + i_x[0] + "v1= " + i_x[2] + "a1= " + y[2]);
        return y;
    }
}