core.math
Class RungeKuttaIntegration

java.lang.Object
  core.math.RungeKuttaIntegration

public class RungeKuttaIntegration

extends java.lang.Object

Runge Kutta Integration 4th order.

Version:

1.0

Author:

Andreas Sundquist, John Belcher

Field Summary

(package private) int	dim The number of first order equations we are integrating.
private VecTimeField	field The derivative matrix of the dependent variables we are integrating.
(package private) double	maxStep The maxstep we take to get to the point requested if stepped is true.
(package private) boolean	stepped If this is true then we step to the requested point in steps of maxstep, and if it is false we step to the requested point directly in the one step requested.
private Vec	x Variables used to compute the stages of the RK step.

Constructor Summary

RungeKuttaIntegration()
Constructor for the straight Runge Kutta 4th order integration.

RungeKuttaIntegration(double maxStep)
Constructor for the stepped Runge Kutta 4th order integration.

Method Summary

private void	ComputeStep(double s, double ds) Compute one RK step from s to s + ds.
void	Evolve(VecTimeField field, Vec x, double s, double ds) Evolve the system from x at s to the new x at x + ds, in one step or a number of small steps, depending on what is requested.
void	SetStep(double maxStep) Sets the maxStep if it has not already been set in the constructor call.

Methods inherited from class java.lang.Object

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

Field Detail

stepped

boolean stepped

If this is true then we step to the requested point in steps of maxstep, and if it is false we step to the requested point directly in the one step requested.

maxStep

double maxStep

The maxstep we take to get to the point requested if stepped is true.

dim

int dim

The number of first order equations we are integrating. That is, this is the number of dependent variables.

x

private Vec x

Variables used to compute the stages of the RK step.

field

private VecTimeField field

The derivative matrix of the dependent variables we are integrating. These are set in the Motion method of the experiment.

Constructor Detail

RungeKuttaIntegration

public RungeKuttaIntegration()

Constructor for the straight Runge Kutta 4th order integration. We step directly to where we want to go in one step.

RungeKuttaIntegration

public RungeKuttaIntegration(double maxStep)

Constructor for the stepped Runge Kutta 4th order integration. We step to where we want to go in steps that do not exceed maxstep.

Parameters:

maxStep - The maximum step we take.

Method Detail

SetStep

public void SetStep(double maxStep)

Sets the maxStep if it has not already been set in the constructor call.

Parameters:

maxStep - The maximum step we can take.

Evolve

public void Evolve(VecTimeField field,
                   Vec x,
                   double s,
                   double ds)

Evolve the system from x at s to the new x at x + ds, in one step or a number of small steps, depending on what is requested. Returns the value of x at x + ds in the value of x. DOES NOT UPDATE THE VALUE OF S TO S + DS!!!!!

Parameters:

field - gives the time derivatives of the variables in x

x - the vector state of the system, which depends on time

s - independent variable, e.g. time

ds - step size in the independent variable

ComputeStep

private void ComputeStep(double s,
                         double ds)

Compute one RK step from s to s + ds. This is the fourth order RK step.

Parameters:

s - the independent variable

ds - the step in the independent variable