public interface EventHandler
Some events can be triggered at discrete times as an ODE problem is solved. This occurs for example when the integration process should be stopped as some state is reached (G-stop facility) when the precise date is unknown a priori, or when the derivatives have discontinuities, or simply when the user wants to monitor some states boundaries crossings.
These events are defined as occurring when a g
switching function sign changes.
Since events are only problem-dependent and are triggered by the independent time variable and the state vector, they can occur at virtually any time, unknown in advance. The integrators will take care to avoid sign changes inside the steps, they will reduce the step size when such an event is detected in order to put this event exactly at the end of the current step. This guarantees that step interpolation (which always has a one step scope) is relevant even in presence of discontinuities. This is independent from the stepsize control provided by integrators that monitor the local error (this event handling feature is available for all integrators, including fixed step ones).
Modifier and Type | Interface and Description |
---|---|
static class |
EventHandler.Action
Enumerate for actions to be performed when an event occurs.
|
Modifier and Type | Field and Description |
---|---|
static int |
DECREASING
Decreasing g-function related events parameter.
|
static int |
INCREASING
Increasing g-function related events parameter.
|
static int |
INCREASING_DECREASING
Both increasing and decreasing g-function related events parameter.
|
Modifier and Type | Method and Description |
---|---|
EventHandler.Action |
eventOccurred(double t,
double[] y,
boolean increasing,
boolean forward)
Handle an event and choose what to do next.
|
double |
g(double t,
double[] y)
Compute the value of the switching function.
|
int |
getSlopeSelection()
Get the parameter in charge of the selection of detected events by the slope of the g-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.
|
boolean |
shouldBeRemoved()
This method is called after the step handler has returned and before the next step is started, but only when
eventOccurred(double, double[], boolean, boolean) has been called. |
static final int INCREASING
static final int DECREASING
static final int INCREASING_DECREASING
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.
t0
- start value of the independent time variabley0
- array containing the start value of the state vectort
- target time for the integrationdouble 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.
t
- current value of the independent time variabley
- array containing the current value of the state vectorEventHandler.Action eventOccurred(double t, double[] y, boolean increasing, boolean forward)
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() 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
.
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)forward
- if true, the integration variable (time) increases during integrationEventHandler.Action.STOP
, EventHandler.Action.RESET_STATE
, EventHandler.Action.RESET_DERIVATIVES
,
EventHandler.Action.CONTINUE
boolean shouldBeRemoved()
This method is called after the step handler has returned and before the next step is started, but only when
eventOccurred(double, double[], boolean, boolean)
has been called.
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
eventOccurred(double, double[], boolean, 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
eventOccurred(double, double[], boolean, boolean)
never returns the EventHandler.Action.RESET_STATE
indicator, this function will never be
called, and it is safe to leave its body empty.
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 arrayint getSlopeSelection()
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