1 /* 2 * Licensed to the Apache Software Foundation (ASF) 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 ASF 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 * http://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.apache.commons.math.ode.events; 19 20 import org.apache.commons.math.ode.FirstOrderDifferentialEquations; 21 import org.apache.commons.math.ode.sampling.StepHandler; 22 23 /** This interface represents a handler for discrete events triggered 24 * during ODE integration. 25 * 26 * <p>Some events can be triggered at discrete times as an ODE problem 27 * is solved. These occurs for example when the integration process 28 * should be stopped as some state is reached (G-stop facility) when the 29 * precise date is unknown a priori, or when the derivatives have 30 * discontinuities, or simply when the user wants to monitor some 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 * @version $Revision: 785473 $ $Date: 2009-06-17 00:02:35 -0400 (Wed, 17 Jun 2009) $ 50 * @since 1.2 51 */ 52 53 public interface EventHandler { 54 55 /** Stop indicator. 56 * <p>This value should be used as the return value of the {@link 57 * #eventOccurred eventOccurred} method when the integration should be 58 * stopped after the event ending the current step.</p> 59 */ 60 public static final int STOP = 0; 61 62 /** Reset state indicator. 63 * <p>This value should be used as the return value of the {@link 64 * #eventOccurred eventOccurred} method when the integration should 65 * go on after the event ending the current step, with a new state 66 * vector (which will be retrieved thanks to the {@link #resetState 67 * resetState} method).</p> 68 */ 69 public static final int RESET_STATE = 1; 70 71 /** Reset derivatives indicator. 72 * <p>This value should be used as the return value of the {@link 73 * #eventOccurred eventOccurred} method when the integration should 74 * go on after the event ending the current step, with a new derivatives 75 * vector (which will be retrieved thanks to the {@link 76 * FirstOrderDifferentialEquations#computeDerivatives} method).</p> 77 */ 78 public static final int RESET_DERIVATIVES = 2; 79 80 /** Continue indicator. 81 * <p>This value should be used as the return value of the {@link 82 * #eventOccurred eventOccurred} method when the integration should go 83 * on after the event ending the current step.</p> 84 */ 85 public static final int CONTINUE = 3; 86 87 /** Compute the value of the switching function. 88 89 * <p>The discrete events are generated when the sign of this 90 * switching function changes. The integrator will take care to change 91 * the stepsize in such a way these events occur exactly at step boundaries. 92 * The switching function must be continuous in its roots neighborhood 93 * (but not necessarily smooth), as the integrator will need to find its 94 * roots to locate precisely the events.</p> 95 96 * @param t current value of the independent <i>time</i> variable 97 * @param y array containing the current value of the state vector 98 * @return value of the g switching function 99 * @exception EventException if the switching function cannot be evaluated 100 */ 101 public double g(double t, double[] y) throws EventException; 102 103 /** Handle an event and choose what to do next. 104 105 * <p>This method is called when the integrator has accepted a step 106 * ending exactly on a sign change of the function, just before the 107 * step handler itself is called. It allows the user to update his 108 * internal data to acknowledge the fact the event has been handled 109 * (for example setting a flag in the {@link 110 * FirstOrderDifferentialEquations differential equations} to switch 111 * the derivatives computation in case of discontinuity), or to 112 * direct the integrator to either stop or continue integration, 113 * possibly with a reset state or derivatives.</p> 114 115 * <ul> 116 * <li>if {@link #STOP} is returned, the step handler will be called 117 * with the <code>isLast</code> flag of the {@link 118 * StepHandler#handleStep handleStep} method set to true and the 119 * integration will be stopped,</li> 120 * <li>if {@link #RESET_STATE} is returned, the {@link #resetState 121 * resetState} method will be called once the step handler has 122 * finished its task, and the integrator will also recompute the 123 * derivatives,</li> 124 * <li>if {@link #RESET_DERIVATIVES} is returned, the integrator 125 * will recompute the derivatives, 126 * <li>if {@link #CONTINUE} is returned, no specific action will 127 * be taken (apart from having called this method) and integration 128 * will continue.</li> 129 * </ul> 130 131 * @param t current value of the independent <i>time</i> variable 132 * @param y array containing the current value of the state vector 133 * @param increasing if true, the value of the switching function increases 134 * when times increases around event (note that increase is measured with respect 135 * to physical time, not with respect to integration which may go backward in time) 136 * @return indication of what the integrator should do next, this 137 * value must be one of {@link #STOP}, {@link #RESET_STATE}, 138 * {@link #RESET_DERIVATIVES} or {@link #CONTINUE} 139 * @exception EventException if the event occurrence triggers an error 140 */ 141 public int eventOccurred(double t, double[] y, boolean increasing) throws EventException; 142 143 /** Reset the state prior to continue the integration. 144 145 * <p>This method is called after the step handler has returned and 146 * before the next step is started, but only when {@link 147 * #eventOccurred} has itself returned the {@link #RESET_STATE} 148 * indicator. It allows the user to reset the state vector for the 149 * next step, without perturbing the step handler of the finishing 150 * step. If the {@link #eventOccurred} never returns the {@link 151 * #RESET_STATE} indicator, this function will never be called, and it is 152 * safe to leave its body empty.</p> 153 154 * @param t current value of the independent <i>time</i> variable 155 * @param y array containing the current value of the state vector 156 * the new state should be put in the same array 157 * @exception EventException if the state cannot be reseted 158 */ 159 public void resetState(double t, double[] y) throws EventException; 160 161 }