Class MidpointStepInterpolator

java.lang.Object

org.apache.commons.math3.ode.sampling.AbstractStepInterpolator

org.apache.commons.math3.ode.nonstiff.RungeKuttaStepInterpolator

org.apache.commons.math3.ode.nonstiff.MidpointStepInterpolator

All Implemented Interfaces:

Externalizable, Serializable, StepInterpolator

class MidpointStepInterpolator
extends RungeKuttaStepInterpolator

This class implements a step interpolator for second order Runge-Kutta integrator.

This interpolator computes dense output inside the last step computed. The interpolation equation is consistent with the integration scheme :

• Using reference point at step start:
  y(t_n + θ h) = y (t_n) + θ h [(1 - θ) y'₁ + θ y'₂]
• Using reference point at step end:
  y(t_n + θ h) = y (t_n + h) + (1-θ) h [θ y'₁ - (1+θ) y'₂]

where θ belongs to [0 ; 1] and where y'₁ and y'₂ are the two evaluations of the derivatives already computed during the step.

Since:

1.2

See Also:

• MidpointIntegrator

Field Summary

Fields

Modifier and Type	Field	Description
private static final long	serialVersionUID	Serializable version identifier

Fields inherited from class RungeKuttaStepInterpolator

integrator, previousState, yDotK

Fields inherited from class AbstractStepInterpolator

currentState, h, interpolatedDerivatives, interpolatedPrimaryDerivatives, interpolatedPrimaryState, interpolatedSecondaryDerivatives, interpolatedSecondaryState, interpolatedState, interpolatedTime

Constructor Summary

Constructors

Constructor	Description
MidpointStepInterpolator()	Simple constructor.
MidpointStepInterpolator(MidpointStepInterpolator interpolator)	Copy constructor.

Method Summary

Modifier and Type	Method	Description
protected void	computeInterpolatedStateAndDerivatives(double theta, double oneMinusThetaH)	Compute the state and derivatives at the interpolated time.
protected StepInterpolator	doCopy()	Really copy the finalized instance.

Methods inherited from class RungeKuttaStepInterpolator

readExternal, reinitialize, shift, writeExternal

Methods inherited from class AbstractStepInterpolator

copy, doFinalize, finalizeStep, getCurrentTime, getGlobalCurrentTime, getGlobalPreviousTime, getInterpolatedDerivatives, getInterpolatedSecondaryDerivatives, getInterpolatedSecondaryState, getInterpolatedState, getInterpolatedTime, getPreviousTime, isForward, readBaseExternal, reinitialize, setInterpolatedTime, setSoftCurrentTime, setSoftPreviousTime, storeTime, writeBaseExternal

Methods inherited from class Object

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

Field Details

serialVersionUID

private static final long serialVersionUID

Serializable version identifier

See Also:

• Constant Field Values

Constructor Details

MidpointStepInterpolator

public MidpointStepInterpolator()

Simple constructor. This constructor builds an instance that is not usable yet, the AbstractStepInterpolator.reinitialize(double[], boolean, EquationsMapper, EquationsMapper[]) method should be called before using the instance in order to initialize the internal arrays. This constructor is used only in order to delay the initialization in some cases. The RungeKuttaIntegrator class uses the prototyping design pattern to create the step interpolators by cloning an uninitialized model and later initializing the copy.

MidpointStepInterpolator

MidpointStepInterpolator(MidpointStepInterpolator interpolator)

Copy constructor.

Parameters:

interpolator - interpolator to copy from. The copy is a deep copy: its arrays are separated from the original arrays of the instance

Method Details

doCopy

protected StepInterpolator doCopy()

Really copy the finalized instance.

This method is called by AbstractStepInterpolator.copy() after the step has been finalized. It must perform a deep copy to have an new instance completely independent for the original instance.

Specified by:

doCopy in class AbstractStepInterpolator

Returns:

a copy of the finalized instance

computeInterpolatedStateAndDerivatives

protected void computeInterpolatedStateAndDerivatives(double theta,
 double oneMinusThetaH)

Compute the state and derivatives at the interpolated time. This is the main processing method that should be implemented by the derived classes to perform the interpolation.

Specified by:

computeInterpolatedStateAndDerivatives in class AbstractStepInterpolator

Parameters:

theta - normalized interpolation abscissa within the step (theta is zero at the previous time step and one at the current time step)

oneMinusThetaH - time gap between the interpolated time and the current time