org.apache.commons.math.ode.sampling

## Class AbstractStepInterpolator

- java.lang.Object
- - org.apache.commons.math.ode.sampling.AbstractStepInterpolator

All Implemented Interfaces:
  java.io.Externalizable, java.io.Serializable, StepInterpolator

Direct Known Subclasses:
  DummyStepInterpolator, GraggBulirschStoerStepInterpolator, NordsieckStepInterpolator, RungeKuttaStepInterpolator

    public abstract class AbstractStepInterpolator
    extends java.lang.Object
    implements StepInterpolator

This abstract class represents an interpolator over the last step during an ODE integration.

The various ODE integrators provide objects extending this class to the step handlers. The handlers can use these objects to retrieve the state vector at intermediate times between the previous and the current grid points (dense output).

Since:
  1.2
Version:
  $Revision: 1073158 $ $Date: 2011-02-21 22:46:52 +0100 (lun. 21 févr. 2011) $
See Also:
  `FirstOrderIntegrator`, `SecondOrderIntegrator`, `StepHandler`, Serialized Form

### Field Summary

Fields
`protected double[]` `currentState` current state
`private boolean` `dirtyState` indicator for dirty state.
`private boolean` `finalized` indicate if the step has been finalized or not.
`private boolean` `forward` integration direction.
`private double` `globalCurrentTime` global current time
`private double` `globalPreviousTime` global previous time
`protected double` `h` current time step
`protected double[]` `interpolatedDerivatives` interpolated derivatives
`protected double[]` `interpolatedState` interpolated state
`protected double` `interpolatedTime` interpolated time
`private double` `softCurrentTime` soft current time
`private double` `softPreviousTime` soft previous time

### Constructor Summary

Constructors
`protected` `AbstractStepInterpolator()` Simple constructor.
`protected` `AbstractStepInterpolator(AbstractStepInterpolator interpolator)` Copy constructor.
`protected` `AbstractStepInterpolator(double[] y, boolean forward)` Simple constructor.

### Method Summary

Methods
`protected abstract void` `computeInterpolatedStateAndDerivatives(double theta, double oneMinusThetaH)` Compute the state and derivatives at the interpolated time.
`StepInterpolator` `copy()` Copy the instance.
`protected abstract StepInterpolator` `doCopy()` Really copy the finalized instance.
`protected void` `doFinalize()` Really finalize the step.
`void` `finalizeStep()` Finalize the step.
`double` `getCurrentTime()` Get the current soft grid point time.
`double` `getGlobalCurrentTime()` Get the current global grid point time.
`double` `getGlobalPreviousTime()` Get the previous global grid point time.
`double[]` `getInterpolatedDerivatives()` Get the derivatives of the state vector of the interpolated point.
`double[]` `getInterpolatedState()` Get the state vector of the interpolated point.
`double` `getInterpolatedTime()` Get the time of the interpolated point.
`double` `getPreviousTime()` Get the previous soft grid point time.
`boolean` `isForward()` Check if the natural integration direction is forward.
`protected double` `readBaseExternal(java.io.ObjectInput in)` Read the base state of the instance.
`abstract void` `readExternal(java.io.ObjectInput in)`
`protected void` `reinitialize(double[] y, boolean isForward)` Reinitialize the instance
`void` `setInterpolatedTime(double time)` Set the time of the interpolated point.
`void` `setSoftCurrentTime(double softCurrentTime)` Restrict step range to a limited part of the global step.
`void` `setSoftPreviousTime(double softPreviousTime)` Restrict step range to a limited part of the global step.
`void` `shift()` Shift one step forward.
`void` `storeTime(double t)` Store the current step time.
`protected void` `writeBaseExternal(java.io.ObjectOutput out)` Save the base state of the instance.
`abstract void` `writeExternal(java.io.ObjectOutput out)`

### Methods inherited from class java.lang.Object

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

### Field Detail

#### h

    protected double h

current time step

#### currentState

    protected double[] currentState

current state

#### interpolatedTime

    protected double interpolatedTime

interpolated time

#### interpolatedState

    protected double[] interpolatedState

interpolated state

#### interpolatedDerivatives

    protected double[] interpolatedDerivatives

interpolated derivatives

#### globalPreviousTime

    private double globalPreviousTime

global previous time

#### globalCurrentTime

    private double globalCurrentTime

global current time

#### softPreviousTime

    private double softPreviousTime

soft previous time

#### softCurrentTime

    private double softCurrentTime

soft current time

#### finalized

    private boolean finalized

indicate if the step has been finalized or not.

#### forward

    private boolean forward

integration direction.

#### dirtyState

    private boolean dirtyState

indicator for dirty state.

### Constructor Detail

#### AbstractStepInterpolator

    protected AbstractStepInterpolator()

Simple constructor. This constructor builds an instance that is not usable yet, the `reinitialize(double[], boolean)` 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. As an example, the `EmbeddedRungeKuttaIntegrator` class uses the prototyping design pattern to create the step interpolators by cloning an uninitialized model and latter initializing the copy.

#### AbstractStepInterpolator

    protected AbstractStepInterpolator(double[] y,
                            boolean forward)

Simple constructor.

Parameters:
  `y` - reference to the integrator array holding the state at the end of the step
  `forward` - integration direction indicator

#### AbstractStepInterpolator

    protected AbstractStepInterpolator(AbstractStepInterpolator interpolator)

Copy constructor.

The copied interpolator should have been finalized before the copy, otherwise the copy will not be able to perform correctly any derivative computation and will throw a `NullPointerException` later. Since we don't want this constructor to throw the exceptions finalization may involve and since we don't want this method to modify the state of the copied interpolator, finalization is not done automatically, it remains under user control.

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

Parameters:
  `interpolator` - interpolator to copy from.

### Method Detail

#### reinitialize

    protected void reinitialize(double[] y,
                    boolean isForward)

Reinitialize the instance

Parameters:
  `y` - reference to the integrator array holding the state at the end of the step
  `isForward` - integration direction indicator

#### copy

    public StepInterpolator copy()
                          throws DerivativeException

Copy the instance.

The copied instance is guaranteed to be independent from the original one. Both can be used with different settings for interpolated time without any side effect.

Specified by:
  `copy` in interface `StepInterpolator`
Returns:
  a deep copy of the instance, which can be used independently.
Throws:
  `DerivativeException` - if user code called from step interpolator finalization triggers one
See Also:
  `StepInterpolator.setInterpolatedTime(double)`

#### doCopy

    protected abstract StepInterpolator doCopy()

Really copy the finalized instance.

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

Returns:
  a copy of the finalized instance

#### shift

    public void shift()

Shift one step forward. Copy the current time into the previous time, hence preparing the interpolator for future calls to `storeTime`

#### storeTime

    public void storeTime(double t)

Store the current step time.

Parameters:
  `t` - current time

#### setSoftPreviousTime

    public void setSoftPreviousTime(double softPreviousTime)

Restrict step range to a limited part of the global step.

This method can be used to restrict a step and make it appear as if the original step was smaller. Calling this method only changes the value returned by `getPreviousTime()`, it does not change any other property

Parameters:
  `softPreviousTime` - start of the restricted step
Since:
  2.2

#### setSoftCurrentTime

    public void setSoftCurrentTime(double softCurrentTime)

Restrict step range to a limited part of the global step.

This method can be used to restrict a step and make it appear as if the original step was smaller. Calling this method only changes the value returned by `getCurrentTime()`, it does not change any other property

Parameters:
  `softCurrentTime` - end of the restricted step
Since:
  2.2

#### getGlobalPreviousTime

    public double getGlobalPreviousTime()

Get the previous global grid point time.

Returns:
  previous global grid point time
Since:
  2.2

#### getGlobalCurrentTime

    public double getGlobalCurrentTime()

Get the current global grid point time.

Returns:
  current global grid point time
Since:
  2.2

#### getPreviousTime

    public double getPreviousTime()

Get the previous soft grid point time.

Specified by:
  `getPreviousTime` in interface `StepInterpolator`
Returns:
  previous soft grid point time
See Also:
  `setSoftPreviousTime(double)`

#### getCurrentTime

    public double getCurrentTime()

Get the current soft grid point time.

Specified by:
  `getCurrentTime` in interface `StepInterpolator`
Returns:
  current soft grid point time
See Also:
  `setSoftCurrentTime(double)`

#### getInterpolatedTime

    public double getInterpolatedTime()

Get the time of the interpolated point. If `StepInterpolator.setInterpolatedTime(double)` has not been called, it returns the current grid point time.

Specified by:
  `getInterpolatedTime` in interface `StepInterpolator`
Returns:
  interpolation point time

#### setInterpolatedTime

    public void setInterpolatedTime(double time)

Set the time of the interpolated point.

Setting the time outside of the current step is now allowed, but should be used with care since the accuracy of the interpolator will probably be very poor far from this step. This allowance has been added to simplify implementation of search algorithms near the step endpoints.

Setting the time changes the instance internal state. If a specific state must be preserved, a copy of the instance must be created using `StepInterpolator.copy()`.

Specified by:
  `setInterpolatedTime` in interface `StepInterpolator`
Parameters:
  `time` - time of the interpolated point

#### isForward

    public boolean isForward()

Check if the natural integration direction is forward.

This method provides the integration direction as specified by the integrator itself, it avoid some nasty problems in degenerated cases like null steps due to cancellation at step initialization, step control or discrete events triggering.

Specified by:
  `isForward` in interface `StepInterpolator`
Returns:
  true if the integration variable (time) increases during integration

#### computeInterpolatedStateAndDerivatives

    protected abstract void computeInterpolatedStateAndDerivatives(double theta,
                                              double oneMinusThetaH)
                                                            throws DerivativeException

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.

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

#### getInterpolatedState

    public double[] getInterpolatedState()
                                  throws DerivativeException

Get the state vector of the interpolated point.

The returned vector is a reference to a reused array, so it should not be modified and it should be copied if it needs to be preserved across several calls.

Specified by:
  `getInterpolatedState` in interface `StepInterpolator`
Returns:
  state vector at time `StepInterpolator.getInterpolatedTime()`
Throws:
  `DerivativeException` - if user code called from step interpolator finalization triggers one
See Also:
  `StepInterpolator.getInterpolatedDerivatives()`

#### getInterpolatedDerivatives

    public double[] getInterpolatedDerivatives()
                                        throws DerivativeException

Get the derivatives of the state vector of the interpolated point.

The returned vector is a reference to a reused array, so it should not be modified and it should be copied if it needs to be preserved across several calls.

Specified by:
  `getInterpolatedDerivatives` in interface `StepInterpolator`
Returns:
  derivatives of the state vector at time `StepInterpolator.getInterpolatedTime()`
Throws:
  `DerivativeException` - if user code called from step interpolator finalization triggers one
See Also:
  `StepInterpolator.getInterpolatedState()`

#### finalizeStep

    public final void finalizeStep()
                            throws DerivativeException

Finalize the step.

Some embedded Runge-Kutta integrators need fewer functions evaluations than their counterpart step interpolators. These interpolators should perform the last evaluations they need by themselves only if they need them. This method triggers these extra evaluations. It can be called directly by the user step handler and it is called automatically if `setInterpolatedTime(double)` is called.

Once this method has been called, no other evaluation will be performed on this step. If there is a need to have some side effects between the step handler and the differential equations (for example update some data in the equations once the step has been done), it is advised to call this method explicitly from the step handler before these side effects are set up. If the step handler induces no side effect, then this method can safely be ignored, it will be called transparently as needed.

Warning: since the step interpolator provided to the step handler as a parameter of the `handleStep` is valid only for the duration of the `handleStep` call, one cannot simply store a reference and reuse it later. One should first finalize the instance, then copy this finalized instance into a new object that can be kept.

This method calls the protected `doFinalize` method if it has never been called during this step and set a flag indicating that it has been called once. It is the `doFinalize` method which should perform the evaluations. This wrapping prevents from calling `doFinalize` several times and hence evaluating the differential equations too often. Therefore, subclasses are not allowed not reimplement it, they should rather reimplement `doFinalize`.

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

#### doFinalize

    protected void doFinalize()
                       throws DerivativeException

Really finalize the step. The default implementation of this method does nothing.

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

#### writeExternal

    public abstract void writeExternal(java.io.ObjectOutput out)
                                throws java.io.IOException

Specified by:
  `writeExternal` in interface `java.io.Externalizable`
Throws:
  `java.io.IOException`

#### readExternal

    public abstract void readExternal(java.io.ObjectInput in)
                               throws java.io.IOException,
                                      java.lang.ClassNotFoundException

Specified by:
  `readExternal` in interface `java.io.Externalizable`
Throws:
  `java.io.IOException`
  `java.lang.ClassNotFoundException`

#### writeBaseExternal

    protected void writeBaseExternal(java.io.ObjectOutput out)
                              throws java.io.IOException

Save the base state of the instance. This method performs step finalization if it has not been done before.

Parameters:
  `out` - stream where to save the state
Throws:
  `java.io.IOException` - in case of write error

#### readBaseExternal

    protected double readBaseExternal(java.io.ObjectInput in)
                               throws java.io.IOException

Read the base state of the instance. This method does neither set the interpolated time nor state. It is up to the derived class to reset it properly calling the `setInterpolatedTime(double)` method later, once all rest of the object state has been set up properly.

Parameters:
  `in` - stream where to read the state from
Returns:
  interpolated time be set later by the caller
Throws:
  `java.io.IOException` - in case of read error