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integrator
Class RungeKutta

java.lang.Object

  integrator.RungeKutta

public class RungeKutta

extends java.lang.Object

Runge Kutta integrator. Inspired by Numerical Recipes in C by Press, William H., Teukolsky, Saul A., Vettering, William T., Flannery, Brian P.

This class keeps the equation to be integrated, initial conditions, eps parameter and other variables. It also has methods to numerically integrate the equation.

Author:

A.K.Nircan

Field Summary
private double[]	ak2
private double[]	ak3
private double[]	ak4
private double[]	ak5
private double[]	ak6
private double	eps
private Equation	eq
(package private) static double	ERRCON
private double	hdid
private double	hmin
private double	hnext
(package private) static int	MAXSTP
private int	nbad
private int	nok
private int	nvar
(package private) static double	PGROW
(package private) static double	PSHRNK
(package private) static double	SAFETY
(package private) static double	TINY
private double	x
private double[]	y
private double[]	yerr
private double[]	ytemp

Constructor Summary
RungeKutta(Equation eq, double eps, double[] ystart, double xstart, double hmin) Constructs the integrator.

Method Summary
Equation	getEq()
double	getHdid()
double	getHnext()
int	getNbad()
int	getNok()
int	getNvar()
double	getX()
double[]	getY()
void	integrate(double step, double stepTry) Integrates Equation eq and takes it from its current state to step ahead.
void	rkCashKrap(double[] dydx, double h, double[] yout) Uses fifth order Cash-Krap Runge-Kutta method to find the solution h steps ahead.
void	rungeKuttaStep(double[] dydx, double htry, double[] yscal) Takes y one step (htry) further.
void	setX(double x) Set current x

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

SAFETY

static final double SAFETY

See Also:

Constant Field Values

PGROW

static final double PGROW

See Also:

Constant Field Values

PSHRNK

static final double PSHRNK

See Also:

Constant Field Values

ERRCON

static final double ERRCON

See Also:

Constant Field Values

MAXSTP

static final int MAXSTP

See Also:

Constant Field Values

TINY

static final double TINY

See Also:

Constant Field Values

x

private double x

y

private double[] y

hdid

private double hdid

hnext

private double hnext

nvar

private int nvar

eq

private Equation eq

eps

private double eps

hmin

private double hmin

nok

private int nok

nbad

private int nbad

yerr

private double[] yerr

ak2

private double[] ak2

ak3

private double[] ak3

ak4

private double[] ak4

ak5

private double[] ak5

ak6

private double[] ak6

ytemp

private double[] ytemp

Constructor Detail

RungeKutta

public RungeKutta(Equation eq,

                  double eps,

                  double[] ystart,

                  double xstart,

                  double hmin)

Constructs the integrator.

Parameters:

eq - Equation to be integrated

eps - sensitivity of the integration

ystart - starting system variables

xstart - starting

hmin - minimum step allowed in integration.

Method Detail

rkCashKrap

public final void rkCashKrap(double[] dydx,

                             double h,

                             double[] yout)

Uses fifth order Cash-Krap Runge-Kutta method to find the solution h steps ahead. Uses class variable y to do the calculation. Updates yout and yerr.

Parameters:

dydx - derivatives.

h - step to be taken.

yout - results at h steps ahead.

rungeKuttaStep

public final void rungeKuttaStep(double[] dydx,

                                 double htry,

                                 double[] yscal)

Takes y one step (htry) further.

Parameters:

dydx - derivatives

htry - step to be taken

yscal - used to calculate error.

integrate

public final void integrate(double step,

                            double stepTry)

Integrates Equation eq and takes it from its current state to step ahead. Method will first try stepTry before adjusting the step.

Parameters:

step - length of the step which will advance x .

stepTry - length of the first trial. stepTry<= step

getNvar

public int getNvar()

Returns:

number of variables

getX

public double getX()

Returns:

the current x

setX

public void setX(double x)

Set current x

Parameters:

x - set

getY

public double[] getY()

Returns:

system variables or results.

getEq

public Equation getEq()

Returns:

equation

getHdid

public double getHdid()

Returns:

step taken.

getHnext

public double getHnext()

Returns:

next step to be taken.

getNbad

public int getNbad()

Returns:

number of bad attempts during integration.

getNok

public int getNok()

Returns:

number of good attempts during integration.

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