org.hipparchus.ode.events.ODEEventHandler Maven / Gradle / Ivy
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* The Hipparchus project licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.hipparchus.ode.events;
import org.hipparchus.ode.ODEState;
import org.hipparchus.ode.ODEStateAndDerivative;
/** 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
* {@link ODEEventDetector} were in this interface (and the remaining
* ones were in the defunct {@code 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 org.hipparchus.ode.events
* @since 3.0
*/
public interface ODEEventHandler {
/** 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
*
* @param initialState initial time, state vector and derivative
* @param finalTime target time for the integration
* @param detector event detector related to the event handler
*/
default void init(ODEStateAndDerivative initialState, double finalTime, ODEEventDetector detector) {
// nothing by default
}
/** 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 {@link
* org.hipparchus.ode.OrdinaryDifferentialEquation
* 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 {@link Action#STOP} is returned, the integration will be stopped,
* - if {@link Action#RESET_STATE} is returned, the {@link #resetState
* resetState} method will be called once the step handler has
* finished its task, and the integrator will also recompute the
* derivatives,
* - if {@link Action#RESET_DERIVATIVES} is returned, the integrator
* will recompute the derivatives,
*
- if {@link Action#RESET_EVENTS} is returned, the integrator
* will recheck all event handlers,
*
- if {@link 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 {@link
* org.hipparchus.ode.sampling.ODEStepHandler ODEStepHandler} method {@link
* org.hipparchus.ode.sampling.ODEStepHandler#handleStep(org.hipparchus.ode.sampling.ODEStateInterpolator)
* handleStep(interpolator)} is to call {@code 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.
*
* @param state current value of the independent time variable, state vector
* and derivative
* @param detector detector that triggered the event
* @param 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)
* @return indication of what the integrator should do next, this
* value must be one of {@link Action#STOP}, {@link Action#RESET_STATE},
* {@link Action#RESET_DERIVATIVES}, {@link Action#RESET_EVENTS}, or
* {@link Action#CONTINUE}
*/
Action eventOccurred(ODEStateAndDerivative state, ODEEventDetector detector, boolean increasing);
/** 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 {@link
* #eventOccurred} has itself returned the {@link 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.
* @param detector detector that triggered the event
* @param state current value of the independent time variable, state vector
* and derivative
* @return reset state (note that it does not include the derivatives, they will
* be added automatically by the integrator afterwards)
*/
default ODEState resetState(ODEEventDetector detector, ODEStateAndDerivative state) {
return state;
}
}