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java.lang.Object org.apache.commons.math.ode.FirstOrderConverter
public class FirstOrderConverter
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.
FirstOrderIntegrator
,
FirstOrderDifferentialEquations
,
SecondOrderDifferentialEquations
Constructor Summary  

FirstOrderConverter(SecondOrderDifferentialEquations equations)
Simple constructor. 
Method Summary  

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 
Constructor Detail 

public FirstOrderConverter(SecondOrderDifferentialEquations equations)
equations
 second order equations set to convertMethod Detail 

public int getDimension()
The dimension of the first order problem is twice the dimension of the underlying second order problem.
getDimension
in interface FirstOrderDifferentialEquations
public void computeDerivatives(double t, double[] y, double[] yDot) throws DerivativeException
computeDerivatives
in interface FirstOrderDifferentialEquations
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
DerivativeException
 this exception is propagated to the caller if the
underlying user function triggers one


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