Class FirstOrderConverter
 java.lang.Object

 org.apache.commons.math.ode.FirstOrderConverter

 All Implemented Interfaces:
FirstOrderDifferentialEquations
public class FirstOrderConverter extends 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 aFirstOrderIntegrator
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 tocomputeSecondDerivatives
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
 See Also:
FirstOrderIntegrator
,FirstOrderDifferentialEquations
,SecondOrderDifferentialEquations


Constructor Summary
Constructors Constructor Description FirstOrderConverter(SecondOrderDifferentialEquations equations)
Simple constructor.

Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method 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.



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 interfaceFirstOrderDifferentialEquations
 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 interfaceFirstOrderDifferentialEquations
 Parameters:
t
 current value of the independent time variabley
 array containing the current value of the state vectoryDot
 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

