Interface EventHandler

public interface EventHandler
This interface represents a handler for discrete events triggered during ODE integration.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 (Gstop 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 problemdependent 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).
 Since:
 1.2


Field Summary
Fields Modifier and Type Field Description static int
CONTINUE
Continue indicator.static int
RESET_DERIVATIVES
Reset derivatives indicator.static int
RESET_STATE
Reset state indicator.static int
STOP
Stop indicator.

Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description int
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
resetState(double t, double[] y)
Reset the state prior to continue the integration.



Field Detail

STOP
static final int STOP
Stop indicator.This value should be used as the return value of the
eventOccurred
method when the integration should be stopped after the event ending the current step. See Also:
 Constant Field Values

RESET_STATE
static final int RESET_STATE
Reset state indicator.This value should be used as the return value of the
eventOccurred
method when the integration should go on after the event ending the current step, with a new state vector (which will be retrieved thanks to theresetState
method). See Also:
 Constant Field Values

RESET_DERIVATIVES
static final int RESET_DERIVATIVES
Reset derivatives indicator.This value should be used as the return value of the
eventOccurred
method when the integration should go on after the event ending the current step, with a new derivatives vector (which will be retrieved thanks to theFirstOrderDifferentialEquations.computeDerivatives(double, double[], double[])
method). See Also:
 Constant Field Values

CONTINUE
static final int CONTINUE
Continue indicator.This value should be used as the return value of the
eventOccurred
method when the integration should go on after the event ending the current step. See Also:
 Constant Field Values


Method Detail

g
double g(double t, double[] y) throws EventException
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.
 Parameters:
t
 current value of the independent time variabley
 array containing the current value of the state vector Returns:
 value of the g switching function
 Throws:
EventException
 if the switching function cannot be evaluated

eventOccurred
int eventOccurred(double t, double[] y, boolean increasing) throws EventException
Handle an event and choose what to do next.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. if
STOP
is returned, the step handler will be called with theisLast
flag of thehandleStep
method set to true and the integration will be stopped,  if
RESET_STATE
is returned, theresetState
method will be called once the step handler has finished its task, and the integrator will also recompute the derivatives,  if
RESET_DERIVATIVES
is returned, the integrator will recompute the derivatives,  if
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
methodhandleStep(interpolator, isLast)
is to call this method first andhandleStep
afterwards. This scheduling allows the integrator to passtrue
as theisLast
parameter to the step handler to make it aware the step will be the last one if this method returnsSTOP
. As the interpolator may be used to navigate back throughout the last step (asStepNormalizer
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 thisEventHandler
interface and theFixedStepHandler
interface, a forward integration may call itseventOccurred
method with t = 10 first and call itshandleStep
method with t = 9 afterwards. Such out of order calls are limited to the size of the integration step forvariable step handlers
and to the size of the fixed step forfixed step handlers
. Parameters:
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) Returns:
 indication of what the integrator should do next, this
value must be one of
STOP
,RESET_STATE
,RESET_DERIVATIVES
orCONTINUE
 Throws:
EventException
 if the event occurrence triggers an error
 if

resetState
void resetState(double t, double[] y) throws EventException
Reset the state prior to continue the integration.This method is called after the step handler has returned and before the next step is started, but only when
eventOccurred(double, double[], boolean)
has itself returned theRESET_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 theeventOccurred(double, double[], boolean)
never returns theRESET_STATE
indicator, this function will never be called, and it is safe to leave its body empty. Parameters:
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 array Throws:
EventException
 if the state cannot be reseted

