Package org.hipparchus.ode.events

Class FieldEventSlopeFilter<T extends FieldODEEventDetector<E>,E extends CalculusFieldElement<E>>

java.lang.Object

org.hipparchus.ode.events.AbstractFieldODEDetector<FieldEventSlopeFilter<T,E>,E>

org.hipparchus.ode.events.FieldEventSlopeFilter<T,E>

Type Parameters:

T - type of the event detector

E - the type of the field elements

All Implemented Interfaces:

FieldODEEventDetector<E>

public class FieldEventSlopeFilter<T extends FieldODEEventDetector<E>,E extends CalculusFieldElement<E>>
extends AbstractFieldODEDetector<FieldEventSlopeFilter<T,E>,E>

Wrapper used to detect only increasing or decreasing events.

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 detector 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 detector 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:

3.0

Field Summary

Fields inherited from class org.hipparchus.ode.events.AbstractFieldODEDetector

DEFAULT_MAX_ITER, DEFAULT_MAXCHECK, DEFAULT_THRESHOLD

Constructor Summary

Constructors

Constructor	Description
FieldEventSlopeFilter(Field<E> field, T rawDetector, FilterType filter)	Wrap a eve,t detector.

Method Summary

Modifier and Type	Method	Description
protected FieldEventSlopeFilter<T,E>	create(FieldAdaptableInterval<E> newMaxCheck, int newMaxIter, BracketedRealFieldUnivariateSolver<E> newSolver, FieldODEEventHandler<E> newHandler)	Build a new instance.
E	g(FieldODEStateAndDerivative<E> state)	Compute the value of the switching function.
T	getDetector()	Get the wrapped raw detector.
void	init(FieldODEStateAndDerivative<E> initialState, E finalTime)	Initialize event handler at the start of an ODE integration.

Methods inherited from class org.hipparchus.ode.events.AbstractFieldODEDetector

getHandler, getMaxCheckInterval, getMaxIterationCount, getSolver, isForward, withHandler, withMaxCheck, withMaxCheck, withMaxIter, withSolver, withThreshold

Methods inherited from class java.lang.Object

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

Constructor Detail

FieldEventSlopeFilter

public FieldEventSlopeFilter(Field<E> field,
                             T rawDetector,
                             FilterType filter)

Wrap a eve,t detector.

Parameters:

field - field to which array elements belong

rawDetector - event detector to wrap

filter - filter to use

Method Detail

create

protected FieldEventSlopeFilter<T,E> create(FieldAdaptableInterval<E> newMaxCheck,
                                                  int newMaxIter,
                                                  BracketedRealFieldUnivariateSolver<E> newSolver,
                                                  FieldODEEventHandler<E> newHandler)

Build a new instance.

Specified by:

create in class AbstractFieldODEDetector<FieldEventSlopeFilter<T extends FieldODEEventDetector<E>,E extends CalculusFieldElement<E>>,E extends CalculusFieldElement<E>>

Parameters:

newMaxCheck - maximum checking interval

newMaxIter - maximum number of iterations in the event time search

newSolver - root-finding algorithm to use to detect state events

newHandler - event handler to call at event occurrences

Returns:

a new instance of the appropriate sub-type

getDetector

public T getDetector()

Get the wrapped raw detector.

Returns:

the wrapped raw detector

init

public void init(FieldODEStateAndDerivative<E> initialState,
                 E finalTime)

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.

The default implementation does nothing

This implementation sets the direction of integration and initializes the event handler. If a subclass overrides this method it should call super.init(s0, t).

Specified by:

init in interface FieldODEEventDetector<T extends FieldODEEventDetector<E>>

Overrides:

init in class AbstractFieldODEDetector<FieldEventSlopeFilter<T extends FieldODEEventDetector<E>,E extends CalculusFieldElement<E>>,E extends CalculusFieldElement<E>>

Parameters:

initialState - initial time, state vector and derivative

finalTime - target time for the integration

g

public E g(FieldODEStateAndDerivative<E> state)

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(state) = h(state) where h is the height above the floor at time state.getTime(). When g(state) 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(state) was decreasing from positive values to 0, and after the event g(state) would be increasing from 0 to positive values again. Consistency is broken here! The solution here is to have g(state) = sign * h(state), where sign is a variable with initial value set to +1. Each time eventOccurred method is called, sign is reset to -sign. This allows the g(state) function to remain continuous (and even smooth) even across events, despite h(state) is not. Basically, the event is used to fold h(state) at bounce points, and sign is used to unfold it back, so the solvers sees a g(state) function which behaves smoothly even across events.

This method is idempotent, that is calling this multiple times with the same state will result in the same value, with two exceptions. First, the definition of the g function may change when an event occurs on the handler, as in the above example. Second, the definition of the g function may change when the event occurs method of any other event handler in the same integrator returns Action.RESET_EVENTS, Action.RESET_DERIVATIVES, or Action.RESET_STATE.

Specified by:

g in interface FieldODEEventDetector<T extends FieldODEEventDetector<E>>

Specified by:

g in class AbstractFieldODEDetector<FieldEventSlopeFilter<T extends FieldODEEventDetector<E>,E extends CalculusFieldElement<E>>,E extends CalculusFieldElement<E>>

Parameters:

state - current value of the independent time variable, state vector and derivative

Returns:

value of the g switching function