Apache Commons Math 3.6.1 · org.apache.commons.math3.ode.events.EventFilter

Modifier and Type	Field and Description
private double	extremeT Extreme time encountered so far.
private final FilterType	filter Filter to use.
private boolean	forward Indicator for forward integration.
private static final int	HISTORY_SIZE Number of past transformers updates stored.
private final EventHandler	rawHandler Wrapped event handler.
private final Transformer[]	transformers Transformers of the g function.
private final double[]	updates Update time of the transformers.

Access	Constructor and Description
public	EventFilter(final EventHandler event handler to wrap rawHandler, final FilterType filter to use filter) Wrap an `event handler`.

Modifier and Type	Method and Description
public EventHandler.Action	eventOccurred(double current value of the independent time variable t, double[] array containing the current value of the state vector y, boolean if true, the value of the switching function increases when times increases around event (note that increase is measured with respect to physical time, not with respect to integration which may go backward in time) increasing) Implements org.apache.commons.math3.ode.events.EventHandler.eventOccurred. Handle an event and choose what to do next.
public double	g(double current value of the independent time variable t, double[] array containing the current value of the state vector y) Implements org.apache.commons.math3.ode.events.EventHandler.g. Compute the value of the switching function.
public void	init(double start value of the independent time variable t0, double[] array containing the start value of the state vector y0, double target time for the integration t) Implements org.apache.commons.math3.ode.events.EventHandler.init. Initialize event handler at the start of an ODE integration.
public void	resetState(double current value of the independent time variable t, double[] array containing the current value of the state vector the new state should be put in the same array y) Implements org.apache.commons.math3.ode.events.EventHandler.resetState. Reset the state prior to continue the integration.

extremeT	back to summary
private double extremeT Extreme time encountered so far.

filter	back to summary
private final FilterType filter Filter to use.

forward	back to summary
private boolean forward Indicator for forward integration.

HISTORY_SIZE	back to summary
private static final int HISTORY_SIZE Number of past transformers updates stored.

rawHandler	back to summary
private final EventHandler rawHandler Wrapped event handler.

transformers	back to summary
private final Transformer[] transformers Transformers of the g function.

updates	back to summary
private final double[] updates Update time of the transformers.

EventFilter	back to summary
public EventFilter(final EventHandler rawHandler, final FilterType filter) Wrap an `event handler`. Parameters rawHandler:EventHandler event handler to wrap filter:FilterType filter to use

Method Detail

eventOccurred back to summary

eventOccurred	back to summary
public EventHandler.Action eventOccurred(double t, double[] y, boolean increasing) Implements org.apache.commons.math3.ode.events.EventHandler.eventOccurred. Doc from org.apache.commons.math3.ode.events.EventHandler.eventOccurred. Handle an event and choose what to do next. This method is called when the integrator has accepted a step ending exactly on a sign change of the function, just before the step handler itself is called (see below for scheduling). It allows the user to update his internal data to acknowledge the fact the event has been handled (for example setting a flag in the `differential equations` to switch the derivatives computation in case of discontinuity), or to direct the integrator to either stop or continue integration, possibly with a reset state or derivatives. if `Action#STOP` is returned, the step handler will be called with the `isLast` flag of the `handleStep` method set to true and the integration will be stopped, if `Action#RESET_STATE` is returned, the `resetState` method will be called once the step handler has finished its task, and the integrator will also recompute the derivatives, if `Action#RESET_DERIVATIVES` is returned, the integrator will recompute the derivatives, if `Action#CONTINUE` is returned, no specific action will be taken (apart from having called this method) and integration will continue. The scheduling between this method and the `StepHandler` method `handleStep(interpolator, isLast)` is to call this method first and `handleStep` afterwards. This scheduling allows the integrator to pass `true` as the `isLast` parameter to the step handler to make it aware the step will be the last one if this method returns `Action#STOP`. As the interpolator may be used to navigate back throughout the last step (as `StepNormalizer` does for example), user code called by this method and user code called by step handlers may experience apparently out of order values of the independent time variable. As an example, if the same user object implements both this `EventHandler` interface and the `FixedStepHandler` interface, a forward integration may call its `eventOccurred` method with t = 10 first and call its `handleStep` method with t = 9 afterwards. Such out of order calls are limited to the size of the integration step for `variable step handlers` and to the size of the fixed step for `fixed step handlers`. Parameters t:double current value of the independent time variable y:double[] array containing the current value of the state vector increasing:boolean if true, the value of the switching function increases when times increases around event (note that increase is measured with respect to physical time, not with respect to integration which may go backward in time) Returns:EventHandler.Action indication of what the integrator should do next, this value must be one of `Action#STOP`, `Action#RESET_STATE`, `Action#RESET_DERIVATIVES` or `Action#CONTINUE`

public EventHandler.Action eventOccurred(double t, double[] y, boolean increasing)

Implements org.apache.commons.math3.ode.events.EventHandler.eventOccurred.

Doc from org.apache.commons.math3.ode.events.EventHandler.eventOccurred.

Handle an event and choose what to do next.

This method is called when the integrator has accepted a step ending exactly on a sign change of the function, just before the step handler itself is called (see below for scheduling). It allows the user to update his internal data to acknowledge the fact the event has been handled (for example setting a flag in the differential equations to switch the derivatives computation in case of discontinuity), or to direct the integrator to either stop or continue integration, possibly with a reset state or derivatives.

if Action#STOP is returned, the step handler will be called with the isLast flag of the handleStep method set to true and the integration will be stopped,
if Action#RESET_STATE is returned, the resetState method will be called once the step handler has finished its task, and the integrator will also recompute the derivatives,
if Action#RESET_DERIVATIVES is returned, the integrator will recompute the derivatives,
if Action#CONTINUE is returned, no specific action will be taken (apart from having called this method) and integration will continue.

The scheduling between this method and the StepHandler method handleStep(interpolator, isLast) is to call this method first and handleStep afterwards. This scheduling allows the integrator to pass true as the isLast parameter to the step handler to make it aware the step will be the last one if this method returns Action#STOP. As the interpolator may be used to navigate back throughout the last step (as StepNormalizer does for example), user code called by this method and user code called by step handlers may experience apparently out of order values of the independent time variable. As an example, if the same user object implements both this EventHandler interface and the FixedStepHandler interface, a forward integration may call its eventOccurred method with t = 10 first and call its handleStep method with t = 9 afterwards. Such out of order calls are limited to the size of the integration step for variable step handlers and to the size of the fixed step for fixed step handlers.

Parameters

t:double: current value of the independent time variable
y:double[]: array containing the current value of the state vector
increasing:boolean: if true, the value of the switching function increases when times increases around event (note that increase is measured with respect to physical time, not with respect to integration which may go backward in time)

Returns:EventHandler.Action

indication of what the integrator should do next, this value must be one of Action#STOP, Action#RESET_STATE, Action#RESET_DERIVATIVES or Action#CONTINUE

g back to summary

g	back to summary
public double g(double t, double[] y) Implements org.apache.commons.math3.ode.events.EventHandler.g. Doc from org.apache.commons.math3.ode.events.EventHandler.g. Compute the value of the switching function. The discrete events are generated when the sign of this switching function changes. The integrator will take care to change the stepsize in such a way these events occur exactly at step boundaries. The switching function must be continuous in its roots neighborhood (but not necessarily smooth), as the integrator will need to find its roots to locate precisely the events. Also note that the integrator expect that once an event has occurred, the sign of the switching function at the start of the next step (i.e. just after the event) is the opposite of the sign just before the event. This consistency between the steps must be preserved, otherwise `exceptions` related to root not being bracketed will occur. This need for consistency is sometimes tricky to achieve. A typical example is using an event to model a ball bouncing on the floor. The first idea to represent this would be to have `g(t) = h(t)` where h is the height above the floor at time `t`. When `g(t)` reaches 0, the ball is on the floor, so it should bounce and the typical way to do this is to reverse its vertical velocity. However, this would mean that before the event `g(t)` was decreasing from positive values to 0, and after the event `g(t)` would be increasing from 0 to positive values again. Consistency is broken here! The solution here is to have `g(t) = sign * h(t)`, where sign is a variable with initial value set to `+1`. Each time `eventOccurred` is called, `sign` is reset to `-sign`. This allows the `g(t)` function to remain continuous (and even smooth) even across events, despite `h(t)` is not. Basically, the event is used to fold `h(t)` at bounce points, and `sign` is used to unfold it back, so the solvers sees a `g(t)` function which behaves smoothly even across events. Parameters t:double current value of the independent time variable y:double[] array containing the current value of the state vector Returns:double value of the g switching function

public double g(double t, double[] y)

Implements org.apache.commons.math3.ode.events.EventHandler.g.

Doc from org.apache.commons.math3.ode.events.EventHandler.g.

Compute the value of the switching function.

The discrete events are generated when the sign of this switching function changes. The integrator will take care to change the stepsize in such a way these events occur exactly at step boundaries. The switching function must be continuous in its roots neighborhood (but not necessarily smooth), as the integrator will need to find its roots to locate precisely the events.

Also note that the integrator expect that once an event has occurred, the sign of the switching function at the start of the next step (i.e. just after the event) is the opposite of the sign just before the event. This consistency between the steps must be preserved, otherwise exceptions related to root not being bracketed will occur.

This need for consistency is sometimes tricky to achieve. A typical example is using an event to model a ball bouncing on the floor. The first idea to represent this would be to have g(t) = h(t) where h is the height above the floor at time t. When g(t) reaches 0, the ball is on the floor, so it should bounce and the typical way to do this is to reverse its vertical velocity. However, this would mean that before the event g(t) was decreasing from positive values to 0, and after the event g(t) would be increasing from 0 to positive values again. Consistency is broken here! The solution here is to have g(t) = sign * h(t), where sign is a variable with initial value set to +1. Each time eventOccurred is called, sign is reset to -sign. This allows the g(t) function to remain continuous (and even smooth) even across events, despite h(t) is not. Basically, the event is used to fold h(t) at bounce points, and sign is used to unfold it back, so the solvers sees a g(t) function which behaves smoothly even across events.

Parameters

t:double: current value of the independent time variable
y:double[]: array containing the current value of the state vector

Returns:double

value of the g switching function

init	back to summary
public void init(double t0, double[] y0, double t) Implements org.apache.commons.math3.ode.events.EventHandler.init. Doc from org.apache.commons.math3.ode.events.EventHandler.init. Initialize event handler at the start of an ODE integration. This method is called once at the start of the integration. It may be used by the event handler to initialize some internal data if needed. Parameters t0:double start value of the independent time variable y0:double[] array containing the start value of the state vector t:double target time for the integration

init

back to summary

public void init(double t0, double[] y0, double t)

Implements org.apache.commons.math3.ode.events.EventHandler.init.

Doc from org.apache.commons.math3.ode.events.EventHandler.init.

Initialize event handler at the start of an ODE integration.

This method is called once at the start of the integration. It may be used by the event handler to initialize some internal data if needed.

Parameters

t0:double: start value of the independent time variable
y0:double[]: array containing the start value of the state vector
t:double: target time for the integration

resetState back to summary

resetState	back to summary
public void resetState(double t, double[] y) Implements org.apache.commons.math3.ode.events.EventHandler.resetState. Doc from org.apache.commons.math3.ode.events.EventHandler.resetState. Reset the state prior to continue the integration. This method is called after the step handler has returned and before the next step is started, but only when `eventOccurred` has itself returned the `Action#RESET_STATE` indicator. It allows the user to reset the state vector for the next step, without perturbing the step handler of the finishing step. If the `eventOccurred` never returns the `Action#RESET_STATE` indicator, this function will never be called, and it is safe to leave its body empty. Parameters t:double current value of the independent time variable y:double[] array containing the current value of the state vector the new state should be put in the same array

public void resetState(double t, double[] y)

Implements org.apache.commons.math3.ode.events.EventHandler.resetState.

Doc from org.apache.commons.math3.ode.events.EventHandler.resetState.

Reset the state prior to continue the integration.

This method is called after the step handler has returned and before the next step is started, but only when eventOccurred has itself returned the Action#RESET_STATE indicator. It allows the user to reset the state vector for the next step, without perturbing the step handler of the finishing step. If the eventOccurred never returns the Action#RESET_STATE indicator, this function will never be called, and it is safe to leave its body empty.

Parameters

t:double: current value of the independent time variable
y:double[]: array containing the current value of the state vector the new state should be put in the same array

public Class EventFilter

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Method Summary

Field Detail

Constructor Detail

Method Detail