org.apache.commons.math.ode

Class FirstOrderConverter

java.lang.Object

org.apache.commons.math.ode.FirstOrderConverter

All Implemented Interfaces:

FirstOrderDifferentialEquations

public class FirstOrderConverter
extends java.lang.Object
implements FirstOrderDifferentialEquations

This class converts second order differential equations to first order ones.

This class is a wrapper around a SecondOrderDifferentialEquations which allow to use a FirstOrderIntegrator to integrate it.

The transformation is done by changing the n dimension state vector to a 2n dimension vector, where the first n components are the initial state variables and the n last components are their first time derivative. The first time derivative of this state vector then really contains both the first and second time derivative of the initial state vector, which can be handled by the underlying second order equations set.

One should be aware that the data is duplicated during the transformation process and that for each call to computeDerivatives, this wrapper does copy 4n scalars : 2n before the call to computeSecondDerivatives in order to dispatch the y state vector into z and zDot, and 2n after the call to gather zDot and zDDot into yDot. Since the underlying problem by itself perhaps also needs to copy data and dispatch the arrays into domain objects, this has an impact on both memory and CPU usage. The only way to avoid this duplication is to perform the transformation at the problem level, i.e. to implement the problem as a first order one and then avoid using this class.

Since:

1.2

Version:

$Revision: 1073158 $ $Date: 2011-02-21 22:46:52 +0100 (lun. 21 févr. 2011) $

See Also:

FirstOrderIntegrator, FirstOrderDifferentialEquations, SecondOrderDifferentialEquations

Field Summary

Fields

Modifier and Type	Field and Description
private int	dimension second order problem dimension.
private SecondOrderDifferentialEquations	equations Underlying second order equations set.
private double[]	z state vector.
private double[]	zDDot second time derivative of the state vector.
private double[]	zDot first time derivative of the state vector.

Constructor Summary

Constructors

Constructor and Description
FirstOrderConverter(SecondOrderDifferentialEquations equations) Simple constructor.

Method Summary

Modifier and Type	Method and Description
void	computeDerivatives(double t, double[] y, double[] yDot) Get the current time derivative of the state vector.
int	getDimension() Get the dimension of the problem.

Methods inherited from class java.lang.Object

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

Field Detail

equations

private final SecondOrderDifferentialEquations equations

Underlying second order equations set.

dimension

private final int dimension

second order problem dimension.

z

private final double[] z

state vector.

zDot

private final double[] zDot

first time derivative of the state vector.

zDDot

private final double[] zDDot

second time derivative of the state vector.

Constructor Detail

FirstOrderConverter

public FirstOrderConverter(SecondOrderDifferentialEquations equations)

Simple constructor. Build a converter around a second order equations set.

Parameters:

equations - second order equations set to convert

Method Detail

getDimension

public int getDimension()

Get the dimension of the problem.

The dimension of the first order problem is twice the dimension of the underlying second order problem.

Specified by:

getDimension in interface FirstOrderDifferentialEquations

Returns:

dimension of the problem

computeDerivatives

public void computeDerivatives(double t,
                               double[] y,
                               double[] yDot)
                        throws DerivativeException

Get the current time derivative of the state vector.

Specified by:

computeDerivatives in interface FirstOrderDifferentialEquations

Parameters:

t - current value of the independent time variable

y - array containing the current value of the state vector

yDot - placeholder array where to put the time derivative of the state vector

Throws:

DerivativeException - this exception is propagated to the caller if the underlying user function triggers one