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 /** This interface represents a handler for discrete events triggered 21 * during ODE integration. 22 * 23 * <p>Some events can be triggered at discrete times as an ODE problem 24 * is solved. This occurs for example when the integration process 25 * should be stopped as some state is reached (G-stop facility) when the 26 * precise date is unknown a priori, or when the derivatives have 27 * discontinuities, or simply when the user wants to monitor some 28 * states boundaries crossings. 29 * </p> 30 * 31 * <p>These events are defined as occurring when a <code>g</code> 32 * switching function sign changes.</p> 33 * 34 * <p>Since events are only problem-dependent and are triggered by the 35 * independent <i>time</i> variable and the state vector, they can 36 * occur at virtually any time, unknown in advance. The integrators will 37 * take care to avoid sign changes inside the steps, they will reduce 38 * the step size when such an event is detected in order to put this 39 * event exactly at the end of the current step. This guarantees that 40 * step interpolation (which always has a one step scope) is relevant 41 * even in presence of discontinuities. This is independent from the 42 * stepsize control provided by integrators that monitor the local 43 * error (this event handling feature is available for all integrators, 44 * including fixed step ones).</p> 45 * 46 * @version $Revision: 1067500 $ $Date: 2011-02-05 21:11:30 +0100 (sam. 05 fvr. 2011) $ 47 * @since 1.2 48 */ 49 50 public interface EventHandler { 51 52 /** Stop indicator. 53 * <p>This value should be used as the return value of the {@link 54 * #eventOccurred eventOccurred} method when the integration should be 55 * stopped after the event ending the current step.</p> 56 */ 57 int STOP = 0; 58 59 /** Reset state indicator. 60 * <p>This value should be used as the return value of the {@link 61 * #eventOccurred eventOccurred} method when the integration should 62 * go on after the event ending the current step, with a new state 63 * vector (which will be retrieved thanks to the {@link #resetState 64 * resetState} method).</p> 65 */ 66 int RESET_STATE = 1; 67 68 /** Reset derivatives indicator. 69 * <p>This value should be used as the return value of the {@link 70 * #eventOccurred eventOccurred} method when the integration should 71 * go on after the event ending the current step, with a new derivatives 72 * vector (which will be retrieved thanks to the {@link 73 * org.apache.commons.math.ode.FirstOrderDifferentialEquations#computeDerivatives} 74 * method).</p> 75 */ 76 int RESET_DERIVATIVES = 2; 77 78 /** Continue indicator. 79 * <p>This value should be used as the return value of the {@link 80 * #eventOccurred eventOccurred} method when the integration should go 81 * on after the event ending the current step.</p> 82 */ 83 int CONTINUE = 3; 84 85 /** Compute the value of the switching function. 86 87 * <p>The discrete events are generated when the sign of this 88 * switching function changes. The integrator will take care to change 89 * the stepsize in such a way these events occur exactly at step boundaries. 90 * The switching function must be continuous in its roots neighborhood 91 * (but not necessarily smooth), as the integrator will need to find its 92 * roots to locate precisely the events.</p> 93 * 94 * @param t current value of the independent <i>time</i> variable 95 * @param y array containing the current value of the state vector 96 * @return value of the g switching function 97 * @exception EventException if the switching function cannot be evaluated 98 */ 99 double g(double t, double[] y) throws EventException; 100 101 /** Handle an event and choose what to do next. 102 103 * <p>This method is called when the integrator has accepted a step 104 * ending exactly on a sign change of the function, just <em>before</em> 105 * the step handler itself is called (see below for scheduling). It 106 * allows the user to update his internal data to acknowledge the fact 107 * the event has been handled (for example setting a flag in the {@link 108 * org.apache.commons.math.ode.FirstOrderDifferentialEquations 109 * differential equations} to switch the derivatives computation in 110 * case of discontinuity), or to direct the integrator to either stop 111 * or continue integration, possibly with a reset state or derivatives.</p> 112 * 113 * <ul> 114 * <li>if {@link #STOP} is returned, the step handler will be called 115 * with the <code>isLast</code> flag of the {@link 116 * org.apache.commons.math.ode.sampling.StepHandler#handleStep handleStep} 117 * method set to true and the integration will be stopped,</li> 118 * <li>if {@link #RESET_STATE} is returned, the {@link #resetState 119 * resetState} method will be called once the step handler has 120 * finished its task, and the integrator will also recompute the 121 * derivatives,</li> 122 * <li>if {@link #RESET_DERIVATIVES} is returned, the integrator 123 * will recompute the derivatives, 124 * <li>if {@link #CONTINUE} is returned, no specific action will 125 * be taken (apart from having called this method) and integration 126 * will continue.</li> 127 * </ul> 128 * 129 * <p>The scheduling between this method and the {@link 130 * org.apache.commons.math.ode.sampling.StepHandler StepHandler} method {@link 131 * org.apache.commons.math.ode.sampling.StepHandler#handleStep( 132 * org.apache.commons.math.ode.sampling.StepInterpolator, boolean) 133 * handleStep(interpolator, isLast)} is to call this method first and 134 * <code>handleStep</code> afterwards. This scheduling allows the integrator to 135 * pass <code>true</code> as the <code>isLast</code> parameter to the step 136 * handler to make it aware the step will be the last one if this method 137 * returns {@link #STOP}. As the interpolator may be used to navigate back 138 * throughout the last step (as {@link 139 * org.apache.commons.math.ode.sampling.StepNormalizer StepNormalizer} 140 * does for example), user code called by this method and user 141 * code called by step handlers may experience apparently out of order values 142 * of the independent time variable. As an example, if the same user object 143 * implements both this {@link EventHandler EventHandler} interface and the 144 * {@link org.apache.commons.math.ode.sampling.FixedStepHandler FixedStepHandler} 145 * interface, a <em>forward</em> integration may call its 146 * <code>eventOccurred</code> method with t = 10 first and call its 147 * <code>handleStep</code> method with t = 9 afterwards. Such out of order 148 * calls are limited to the size of the integration step for {@link 149 * org.apache.commons.math.ode.sampling.StepHandler variable step handlers} and 150 * to the size of the fixed step for {@link 151 * org.apache.commons.math.ode.sampling.FixedStepHandler fixed step handlers}.</p> 152 * 153 * @param t current value of the independent <i>time</i> variable 154 * @param y array containing the current value of the state vector 155 * @param increasing if true, the value of the switching function increases 156 * when times increases around event (note that increase is measured with respect 157 * to physical time, not with respect to integration which may go backward in time) 158 * @return indication of what the integrator should do next, this 159 * value must be one of {@link #STOP}, {@link #RESET_STATE}, 160 * {@link #RESET_DERIVATIVES} or {@link #CONTINUE} 161 * @exception EventException if the event occurrence triggers an error 162 */ 163 int eventOccurred(double t, double[] y, boolean increasing) throws EventException; 164 165 /** Reset the state prior to continue the integration. 166 167 * <p>This method is called after the step handler has returned and 168 * before the next step is started, but only when {@link 169 * #eventOccurred} has itself returned the {@link #RESET_STATE} 170 * indicator. It allows the user to reset the state vector for the 171 * next step, without perturbing the step handler of the finishing 172 * step. If the {@link #eventOccurred} never returns the {@link 173 * #RESET_STATE} indicator, this function will never be called, and it is 174 * safe to leave its body empty.</p> 175 * 176 * @param t current value of the independent <i>time</i> variable 177 * @param y array containing the current value of the state vector 178 * the new state should be put in the same array 179 * @exception EventException if the state cannot be reseted 180 */ 181 void resetState(double t, double[] y) throws EventException; 182 183 } 184
