Class EventFilter
- All Implemented Interfaces:
EventHandler
General events
are defined implicitly
by a g function
crossing
zero. This function needs to be continuous in the event neighborhood,
and its sign must remain consistent between events. This implies that
during an ODE integration, events triggered are alternately events
for which the function increases from negative to positive values,
and events for which the function decreases from positive to
negative values.
Sometimes, users are only interested in one type of event (say increasing events for example) and not in the other type. In these cases, looking precisely for all events location and triggering events that will later be ignored is a waste of computing time.
Users can wrap a regular event handler
in
an instance of this class and provide this wrapping instance to
the ODE solver
in order to avoid wasting time looking for uninteresting events.
The wrapper will intercept the calls to the g function
and to the eventOccurred
method in order to ignore uninteresting events. The
wrapped regular event handler
will the see only
the interesting events, i.e. either only increasing
events or
decreasing
events. the number of calls to the g function
will also be reduced.
- Since:
- 3.2
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Nested Class Summary
Nested classes/interfaces inherited from interface org.apache.commons.math3.ode.events.EventHandler
EventHandler.Action
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Field Summary
FieldsModifier and TypeFieldDescriptionprivate double
Extreme time encountered so far.private final FilterType
Filter to use.private boolean
Indicator for forward integration.private static final int
Number of past transformers updates stored.private final EventHandler
Wrapped event handler.private final Transformer[]
Transformers of the g function.private final double[]
Update time of the transformers. -
Constructor Summary
ConstructorsConstructorDescriptionEventFilter
(EventHandler rawHandler, FilterType filter) Wrap anevent handler
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Method Summary
Modifier and TypeMethodDescriptioneventOccurred
(double t, double[] y, boolean increasing) Handle an event and choose what to do next.double
g
(double t, double[] y) Compute the value of the switching function.void
init
(double t0, double[] y0, double t) Initialize event handler at the start of an ODE integration.void
resetState
(double t, double[] y) Reset the state prior to continue the integration.
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Field Details
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HISTORY_SIZE
private static final int HISTORY_SIZENumber of past transformers updates stored.- See Also:
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rawHandler
Wrapped event handler. -
filter
Filter to use. -
transformers
Transformers of the g function. -
updates
private final double[] updatesUpdate time of the transformers. -
forward
private boolean forwardIndicator for forward integration. -
extremeT
private double extremeTExtreme time encountered so far.
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Constructor Details
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EventFilter
Wrap anevent handler
.- Parameters:
rawHandler
- event handler to wrapfilter
- filter to use
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Method Details
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init
public void init(double t0, double[] y0, double t) 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.
- Specified by:
init
in interfaceEventHandler
- Parameters:
t0
- start value of the independent time variabley0
- array containing the start value of the state vectort
- target time for the integration
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g
public double g(double t, double[] y) 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 timet
. Wheng(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 eventg(t)
was decreasing from positive values to 0, and after the eventg(t)
would be increasing from 0 to positive values again. Consistency is broken here! The solution here is to haveg(t) = sign * h(t)
, where sign is a variable with initial value set to+1
. Each timeeventOccurred
is called,sign
is reset to-sign
. This allows theg(t)
function to remain continuous (and even smooth) even across events, despiteh(t)
is not. Basically, the event is used to foldh(t)
at bounce points, andsign
is used to unfold it back, so the solvers sees ag(t)
function which behaves smoothly even across events.- Specified by:
g
in interfaceEventHandler
- Parameters:
t
- current value of the independent time variabley
- array containing the current value of the state vector- Returns:
- value of the g switching function
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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
EventHandler.Action.STOP
is returned, the step handler will be called with theisLast
flag of thehandleStep
method set to true and the integration will be stopped, - if
EventHandler.Action.RESET_STATE
is returned, theresetState
method will be called once the step handler has finished its task, and the integrator will also recompute the derivatives, - if
EventHandler.Action.RESET_DERIVATIVES
is returned, the integrator will recompute the derivatives, - if
EventHandler.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
methodhandleStep(interpolator, isLast)
is to call this method first andhandleStep
afterwards. This scheduling allows the integrator to passtrue
as theisLast
parameter to the step handler to make it aware the step will be the last one if this method returnsEventHandler.Action.STOP
. As the interpolator may be used to navigate back throughout the last step (asStepNormalizer
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 thisEventHandler
interface and theFixedStepHandler
interface, a forward integration may call itseventOccurred
method with t = 10 first and call itshandleStep
method with t = 9 afterwards. Such out of order calls are limited to the size of the integration step forvariable step handlers
and to the size of the fixed step forfixed step handlers
.- Specified by:
eventOccurred
in interfaceEventHandler
- Parameters:
t
- current value of the independent time variabley
- array containing the current value of the state vectorincreasing
- 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:
- indication of what the integrator should do next, this
value must be one of
EventHandler.Action.STOP
,EventHandler.Action.RESET_STATE
,EventHandler.Action.RESET_DERIVATIVES
orEventHandler.Action.CONTINUE
- if
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resetState
public void resetState(double t, double[] y) 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
EventHandler.eventOccurred(double, double[], boolean)
has itself returned theEventHandler.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 theEventHandler.eventOccurred(double, double[], boolean)
never returns theEventHandler.Action.RESET_STATE
indicator, this function will never be called, and it is safe to leave its body empty.- Specified by:
resetState
in interfaceEventHandler
- Parameters:
t
- current value of the independent time variabley
- array containing the current value of the state vector the new state should be put in the same array
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