Class EventSlopeFilter<T extends ODEEventDetector>
 Type Parameters:
T
 type of the event detector
 All Implemented Interfaces:
ODEEventDetector
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 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:
 3.0

Field Summary
Fields inherited from class org.hipparchus.ode.events.AbstractODEDetector
DEFAULT_MAX_ITER, DEFAULT_MAXCHECK, DEFAULT_THRESHOLD

Constructor Summary

Method Summary
Modifier and TypeMethodDescriptionprotected EventSlopeFilter<T>
create
(AdaptableInterval newMaxCheck, int newMaxIter, BracketedUnivariateSolver<UnivariateFunction> newSolver, ODEEventHandler newHandler) Build a new instance.double
g
(ODEStateAndDerivative state) Compute the value of the switching function.Get the wrapped raw detector.void
init
(ODEStateAndDerivative initialState, double finalTime) Initialize event handler at the start of an ODE integration.Methods inherited from class org.hipparchus.ode.events.AbstractODEDetector
getHandler, getMaxCheckInterval, getMaxIterationCount, getSolver, isForward, withHandler, withMaxCheck, withMaxCheck, withMaxIter, withSolver, withThreshold

Constructor Details

EventSlopeFilter
Wrap anevent detector
. Parameters:
rawDetector
 event detector to wrapfilter
 filter to use Since:
 3.0


Method Details

create
protected EventSlopeFilter<T> create(AdaptableInterval newMaxCheck, int newMaxIter, BracketedUnivariateSolver<UnivariateFunction> newSolver, ODEEventHandler newHandler) Build a new instance. Specified by:
create
in classAbstractODEDetector<EventSlopeFilter<T extends ODEEventDetector>>
 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 interfaceODEEventDetector
 Overrides:
init
in classAbstractODEDetector<EventSlopeFilter<T extends ODEEventDetector>>
 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 for the integrator to detect an event the sign of the switching function must have opposite signs just before and after the event. If this consistency is not preserved the integrator may not detect any events.
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
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 theeventOccurred
method of any other event handler in the same integrator returnsAction.RESET_EVENTS
,Action.RESET_DERIVATIVES
, orAction.RESET_STATE
. Specified by:
g
in interfaceODEEventDetector
 Specified by:
g
in classAbstractODEDetector<EventSlopeFilter<T extends ODEEventDetector>>
 Parameters:
state
 current value of the independent time variable, state vector and derivative Returns:
 value of the g switching function
 See Also:
