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public interface SwitchingFunction
This interface represents a switching function.
A switching function allows to handle discrete events in
integration problems. These events occur for example when the
integration process should be stopped as some value is reached
(G-stop facility), or when the derivatives have
discontinuities, or simply when the user wants to monitor some
states boundaries crossings. These events are traditionally defined
as occurring when a g
function sign changes, hence
the name switching functions.
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 feature is available on 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)
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 FunctionEvaluationException
Discrete events are generated when the sign of this function changes, the integrator will take care to change the stepsize in such a way these events occur exactly at step boundaries. This function must be continuous (at least in its roots neighborhood), as the integrator will need to find its roots to locate the events.
t
- current value of the independent time variabley
- array containing the current value of the state vector
FunctionEvaluationException
- if the value of the function
cannot be evaluatedint eventOccurred(double t, double[] y)
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. 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.
t
- current value of the independent time variabley
- array containing the current value of the state vector
STOP
, RESET_STATE
,
RESET_DERIVATIVES
or CONTINUE
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[])
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[])
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
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