1 /*
2 * Licensed to the Hipparchus project under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The Hipparchus project licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * https://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18 package org.hipparchus.ode.events;
19
20 import org.hipparchus.CalculusFieldElement;
21 import org.hipparchus.ode.FieldODEState;
22 import org.hipparchus.ode.FieldODEStateAndDerivative;
23
24 /** This interface represents a handler for discrete events triggered
25 * during ODE integration.
26 *
27 * <p>Some events can be triggered at discrete times as an ODE problem
28 * is solved. This occurs for example when the integration process
29 * should be stopped as some state is reached (G-stop facility) when the
30 * precise date is unknown a priori, or when the derivatives have
31 * states boundaries crossings.
32 * </p>
33 *
34 * <p>These events are defined as occurring when a <code>g</code>
35 * switching function sign changes.</p>
36 *
37 * <p>Since events are only problem-dependent and are triggered by the
38 * independent <i>time</i> variable and the state vector, they can
39 * occur at virtually any time, unknown in advance. The integrators will
40 * take care to avoid sign changes inside the steps, they will reduce
41 * the step size when such an event is detected in order to put this
42 * event exactly at the end of the current step. This guarantees that
43 * step interpolation (which always has a one step scope) is relevant
44 * even in presence of discontinuities. This is independent from the
45 * stepsize control provided by integrators that monitor the local
46 * error (this event handling feature is available for all integrators,
47 * including fixed step ones).</p>
48 *
49 * <p>
50 * Note that prior to Hipparchus 3.0, some of the methods that are now in
51 * {@link FieldODEEventDetector} were in this interface (and the remaining
52 * ones were in the defunct {@code FieldEventHandlerConfiguration} interface).
53 * The interfaces have been reorganized to allow different objects to be
54 * used in event detection and event handling, hence allowing users to
55 * reuse predefined events detectors with custom handlers.
56 * </p>
57 * @see org.hipparchus.ode.events
58 * @param <T> the type of the field elements
59 */
60 public interface FieldODEEventHandler<T extends CalculusFieldElement<T>> {
61
62 /** Initialize event handler at the start of an ODE integration.
63 * <p>
64 * This method is called once at the start of the integration. It
65 * may be used by the event handler to initialize some internal data
66 * if needed.
67 * </p>
68 * <p>
69 * The default implementation does nothing
70 * </p>
71 * @param initialState initial time, state vector and derivative
72 * @param finalTime target time for the integration
73 * @param detector event detector related to the event handler
74 */
75 default void init(FieldODEStateAndDerivative<T> initialState, T finalTime, FieldODEEventDetector<T> detector) {
76 // nothing by default
77 }
78
79 /** Handle an event and choose what to do next.
80
81 * <p>This method is called when the integrator has accepted a step
82 * ending exactly on a sign change of the function, just <em>after</em>
83 * the step handler itself is called (see below for scheduling). It
84 * allows the user to update his internal data to acknowledge the fact
85 * the event has been handled (for example setting a flag in the {@link
86 * org.hipparchus.ode.FieldOrdinaryDifferentialEquation
87 * differential equations} to switch the derivatives computation in
88 * case of discontinuity), or to direct the integrator to either stop
89 * or continue integration, possibly with a reset state or derivatives.</p>
90 *
91 * <ul>
92 * <li>if {@link Action#STOP} is returned, the integration will be stopped,</li>
93 * <li>if {@link Action#RESET_STATE} is returned, the {@link #resetState
94 * resetState} method will be called once the step handler has
95 * finished its task, and the integrator will also recompute the
96 * derivatives,</li>
97 * <li>if {@link Action#RESET_DERIVATIVES} is returned, the integrator
98 * will recompute the derivatives,
99 * <li>if {@link Action#RESET_EVENTS} is returned, the integrator
100 * will recheck all event handlers,
101 * <li>if {@link Action#CONTINUE} is returned, no specific action will
102 * be taken (apart from having called this method) and integration
103 * will continue.</li>
104 * </ul>
105 *
106 * <p>The scheduling between this method and the {@link
107 * org.hipparchus.ode.sampling.FieldODEStepHandler FieldODEStepHandler} method {@link
108 * org.hipparchus.ode.sampling.FieldODEStepHandler#handleStep
109 * handleStep(interpolator, isLast)} is to call {@code handleStep} first and this method afterwards
110 * (this scheduling changed as of Hipparchus 2.0). This scheduling allows user code
111 * called by this method and user code called by step handlers to get values
112 * of the independent time variable consistent with integration direction.</p>
113 *
114 * @param state current value of the independent <i>time</i> variable, state vector
115 * and derivative
116 * @param detector detector that triggered the event
117 * @param increasing if true, the value of the switching function increases
118 * when times increases around event (note that increase is measured with respect
119 * to physical time, not with respect to integration which may go backward in time)
120 * @return indication of what the integrator should do next, this
121 * value must be one of {@link Action#STOP}, {@link Action#RESET_STATE},
122 * {@link Action#RESET_DERIVATIVES}, {@link Action#RESET_EVENTS}, or
123 * {@link Action#CONTINUE}
124 */
125 Action eventOccurred(FieldODEStateAndDerivative<T> state, FieldODEEventDetector<T> detector, boolean increasing);
126
127 /** Reset the state prior to continue the integration.
128
129 * <p>This method is called after the step handler has returned and
130 * before the next step is started, but only when {@link
131 * #eventOccurred(FieldODEStateAndDerivative, FieldODEEventDetector, boolean) eventOccurred}
132 * has itself returned the {@link Action#RESET_STATE} indicator. It allows the user to reset
133 * the state vector for the next step, without perturbing the step handler of the
134 * finishing step.</p>
135 * <p>The default implementation returns its argument.</p>
136 * @param detector detector that triggered the event
137 * @param state current value of the independent <i>time</i> variable, state vector
138 * and derivative
139 * @return reset state (note that it does not include the derivatives, they will
140 * be added automatically by the integrator afterwards)
141 */
142 default FieldODEState<T> resetState(FieldODEEventDetector<T> detector, FieldODEStateAndDerivative<T> state) {
143 return state;
144 }
145
146 }