Interface ODEEventHandler

public interface ODEEventHandler
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 (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).

Note that prior to Hipparchus 3.0, some of the methods that are now in ODEEventDetector were in this interface (and the remaining ones were in the defunct EventHandlerConfiguration interface). The interfaces have been reorganized to allow different objects to be used in event detection and event handling, hence allowing users to reuse predefined events detectors with custom handlers.

See Also:
  • Method Details

    • init

      default void init(ODEStateAndDerivative initialState, double finalTime, ODEEventDetector detector)
      Initialize event handler at the start of an ODE integration.

      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.

      The default implementation does nothing

      initialState - initial time, state vector and derivative
      finalTime - target time for the integration
      detector - event detector related to the event handler
    • eventOccurred

      Action eventOccurred(ODEStateAndDerivative state, ODEEventDetector detector, boolean increasing)
      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 after 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 Action.STOP is returned, the integration will be stopped,
      • if 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,
      • if Action.RESET_DERIVATIVES is returned, the integrator will recompute the derivatives,
      • if Action.RESET_EVENTS is returned, the integrator will recheck all event handlers,
      • if 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 ODEStepHandler method handleStep(interpolator) is to call handleStep first and this method afterwards (this scheduling changed as of Hipparchus 2.0). This scheduling allows user code called by this method and user code called by step handlers to get values of the independent time variable consistent with integration direction.

      state - current value of the independent time variable, state vector and derivative
      detector - detector that triggered the event
      increasing - 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)
      indication of what the integrator should do next, this value must be one of Action.STOP, Action.RESET_STATE, Action.RESET_DERIVATIVES, Action.RESET_EVENTS, or Action.CONTINUE
    • resetState

      default ODEState resetState(ODEEventDetector detector, ODEStateAndDerivative state)
      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(org.hipparchus.ode.ODEStateAndDerivative,, boolean) has itself returned the 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.

      The default implementation returns its argument.

      detector - detector that triggered the event
      state - current value of the independent time variable, state vector and derivative
      reset state (note that it does not include the derivatives, they will be added automatically by the integrator afterwards)