org.jscience.mathematics.analysis.ode
Interface SwitchingFunction

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 has discontinuities. These events are traditionally defined as occurring when a g function sign changes.

Since events are only problem-dependent and are triggered by the independant time variable and the state vector, they can occur at virtually any time. 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 Reset 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

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

static final int RESET

Reset 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 through the resetState 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)

Compute the value of the switching function.

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, as the integrator will need to find its roots to locate the events.

Parameters:

t - current value of the independant time variable

y - array containing the current value of the state vector

Returns:

value of the g function

eventOccurred

int eventOccurred(double t,
                  double[] y)

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. It allows the user to update his internal data to acknowledge the fact the event has been handled (for example setting a flag to switch the derivatives computation in case of discontinuity), and it allows to direct the integrator to either stop or continue integration, possibly with a reset state.

If STOP is returned, the step handler will be called with the isLast flag of the handleStep method set to true. If RESET is returned, the resetState method will be called once the step handler has finished its task.

Parameters:

t - current value of the independant time variable

y - array containing the current value of the state vector

Returns:

indication of what the integrator should do next, this value must be one of STOP, RESET or CONTINUE

resetState

void resetState(double t,
                double[] y)

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[]) has itself returned the RESET 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 indicator, this function will never be called, and it is safe to leave its body empty.

Parameters:

t - current value of the independant time variable

y - array containing the current value of the state vector the new state should be put in the same array