public class EventFilter extends Object implements 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.
EventHandler.Action| Constructor and Description | 
|---|
| EventFilter(EventHandler rawHandler,
           FilterType filter)Wrap an  event handler. | 
| Modifier and Type | Method and Description | 
|---|---|
| EventHandler.Action | eventOccurred(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. | 
public EventFilter(EventHandler rawHandler, FilterType filter)
event handler.rawHandler - event handler to wrapfilter - filter to usepublic void init(double t0,
        double[] y0,
        double t)
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.
init in interface EventHandlert0 - start value of the independent time variabley0 - array containing the start value of the state vectort - target time for the integrationpublic double g(double t,
       double[] y)
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 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.
g in interface EventHandlert - current value of the independent time variabley - array containing the current value of the state vectorpublic EventHandler.Action eventOccurred(double t, double[] y, boolean increasing)
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.
EventHandler.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,EventHandler.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,EventHandler.Action.RESET_DERIVATIVES is returned, the integrator
   will recompute the derivatives,
   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 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 EventHandler.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.
eventOccurred in interface EventHandlert - 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)EventHandler.Action.STOP, EventHandler.Action.RESET_STATE,
 EventHandler.Action.RESET_DERIVATIVES or EventHandler.Action.CONTINUEpublic void resetState(double t,
              double[] y)
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 the EventHandler.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 EventHandler.eventOccurred(double, double[], boolean) never returns the EventHandler.Action.RESET_STATE indicator, this function will never be called, and it is
 safe to leave its body empty.
resetState in interface EventHandlert - 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 arrayCopyright © 2003–2016 The Apache Software Foundation. All rights reserved.