Class FieldEventSlopeFilter<T extends FieldODEEventDetector<E>,E extends CalculusFieldElement<E>>
 Type Parameters:
T
 type of the event detectorE
 the type of the field elements
 All Implemented Interfaces:
FieldODEEventDetector<E>
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
ConstructorDescriptionFieldEventSlopeFilter
(Field<E> field, T rawDetector, FilterType filter) Wrap aeve,t detector
. 
Method Summary
Modifier and TypeMethodDescriptionprotected FieldEventSlopeFilter<T,
E> create
(FieldAdaptableInterval<E> newMaxCheck, int newMaxIter, BracketedRealFieldUnivariateSolver<E> newSolver, FieldODEEventHandler<E> newHandler) Build a new instance.g
(FieldODEStateAndDerivative<E> state) Compute the value of the switching function.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

Constructor Details

FieldEventSlopeFilter
Wrap aeve,t detector
. Parameters:
field
 field to which array elements belongrawDetector
 event detector to wrapfilter
 filter to use


Method Details

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 classAbstractFieldODEDetector<FieldEventSlopeFilter<T extends FieldODEEventDetector<E>,
E extends CalculusFieldElement<E>>, E extends CalculusFieldElement<E>>  Parameters:
newMaxCheck
 maximum checking intervalnewMaxIter
 maximum number of iterations in the event time searchnewSolver
 rootfinding algorithm to use to detect state eventsnewHandler
 event handler to call at event occurrences Returns:
 a new instance of the appropriate subtype

getDetector
Get the wrapped raw detector. Returns:
 the wrapped raw detector

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.
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 interfaceFieldODEEventDetector<T extends FieldODEEventDetector<E>>
 Overrides:
init
in classAbstractFieldODEDetector<FieldEventSlopeFilter<T extends FieldODEEventDetector<E>,
E extends CalculusFieldElement<E>>, E extends CalculusFieldElement<E>>  Parameters:
initialState
 initial time, state vector and derivativefinalTime
 target time for the integration

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(state) = h(state)
where h is the height above the floor at timestate.getTime()
. Wheng(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 eventg(state)
was decreasing from positive values to 0, and after the eventg(state)
would be increasing from 0 to positive values again. Consistency is broken here! The solution here is to haveg(state) = sign * h(state)
, where sign is a variable with initial value set to+1
. Each timeeventOccurred
method is called,sign
is reset tosign
. This allows theg(state)
function to remain continuous (and even smooth) even across events, despiteh(state)
is not. Basically, the event is used to foldh(state)
at bounce points, andsign
is used to unfold it back, so the solvers sees ag(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 theevent occurs
method of any other event handler in the same integrator returnsAction.RESET_EVENTS
,Action.RESET_DERIVATIVES
, orAction.RESET_STATE
. Specified by:
g
in interfaceFieldODEEventDetector<T extends FieldODEEventDetector<E>>
 Specified by:
g
in classAbstractFieldODEDetector<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
