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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).
Field Summary  

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  

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 

static final int STOP
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.
static final int RESET_STATE
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 the resetState
method).
static final int RESET_DERIVATIVES
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 the FirstOrderDifferentialEquations.computeDerivatives(double, double[], double[])
method).
static final int CONTINUE
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.
Method Detail 

double g(double t, double[] y) throws EventException
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 vector
EventException
 if the switching function cannot be evaluatedint eventOccurred(double t, double[] y, boolean increasing) throws EventException
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.
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,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,RESET_DERIVATIVES
is returned, the integrator
will recompute the derivatives,
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(interpolator, isLast)
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 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)
STOP
, RESET_STATE
,
RESET_DERIVATIVES
or CONTINUE
EventException
 if the event occurrence triggers an errorvoid resetState(double t, double[] y) throws EventException
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 the 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)
never returns the 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 array
EventException
 if the state cannot be reseted


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