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.jacobians; 19 20 import org.apache.commons.math.ode.events.EventException; 21 22 /** This interface represents a handler for discrete events triggered 23 * during ODE integration. 24 * 25 * <p>Some events can be triggered at discrete times as an ODE problem 26 * is solved. This occurs for example when the integration process 27 * should be stopped as some state is reached (G-stop facility) when the 28 * precise date is unknown a priori, or when the derivatives have 29 * discontinuities, or simply when the user wants to monitor some 30 * states boundaries crossings. 31 * </p> 32 * 33 * <p>These events are defined as occurring when a <code>g</code> 34 * switching function sign changes.</p> 35 * 36 * <p>Since events are only problem-dependent and are triggered by the 37 * independent <i>time</i> variable and the state vector, they can 38 * occur at virtually any time, unknown in advance. The integrators will 39 * take care to avoid sign changes inside the steps, they will reduce 40 * the step size when such an event is detected in order to put this 41 * event exactly at the end of the current step. This guarantees that 42 * step interpolation (which always has a one step scope) is relevant 43 * even in presence of discontinuities. This is independent from the 44 * stepsize control provided by integrators that monitor the local 45 * error (this event handling feature is available for all integrators, 46 * including fixed step ones).</p> 47 * 48 * <p>Note that is is possible to register a {@link 49 * org.apache.commons.math.ode.events.EventHandler classical event handler} 50 * in the low level integrator used to build a {@link FirstOrderIntegratorWithJacobians} 51 * rather than implementing this class. The event handlers registered at low level 52 * will see the big compound state whether the event handlers defined by this interface 53 * see the original state, and its jacobians in separate arrays.</p> 54 * 55 * <p>The compound state is guaranteed to contain the original state in the first 56 * elements, followed by the jacobian with respect to initial state (in row order), 57 * followed by the jacobian with respect to parameters (in row order). If for example 58 * the original state dimension is 6 and there are 3 parameters, the compound state will 59 * be a 60 elements array. The first 6 elements will be the original state, the next 36 60 * elements will be the jacobian with respect to initial state, and the remaining 18 elements 61 * will be the jacobian with respect to parameters.</p> 62 * 63 * <p>Dealing with low level event handlers is cumbersome if one really needs the jacobians 64 * in these methods, but it also prevents many data being copied back and forth between 65 * state and jacobians on one side and compound state on the other side. So for performance 66 * reasons, it is recommended to use this interface <em>only</em> if jacobians are really 67 * needed and to use lower level handlers if only state is needed.</p> 68 * 69 * @version $Revision: 1037341 $ $Date: 2010-11-20 22:58:35 +0100 (sam. 20 nov. 2010) $ 70 * @since 2.1 71 * @deprecated as of 2.2 the complete package is deprecated, it will be replaced 72 * in 3.0 by a completely rewritten implementation 73 */ 74 @Deprecated 75 public interface EventHandlerWithJacobians { 76 77 /** Stop indicator. 78 * <p>This value should be used as the return value of the {@link 79 * #eventOccurred eventOccurred} method when the integration should be 80 * stopped after the event ending the current step.</p> 81 */ 82 int STOP = 0; 83 84 /** Reset state indicator. 85 * <p>This value should be used as the return value of the {@link 86 * #eventOccurred eventOccurred} method when the integration should 87 * go on after the event ending the current step, with a new state 88 * vector (which will be retrieved thanks to the {@link #resetState 89 * resetState} method).</p> 90 */ 91 int RESET_STATE = 1; 92 93 /** Reset derivatives indicator. 94 * <p>This value should be used as the return value of the {@link 95 * #eventOccurred eventOccurred} method when the integration should 96 * go on after the event ending the current step, with a new derivatives 97 * vector (which will be retrieved thanks to the {@link 98 * org.apache.commons.math.ode.FirstOrderDifferentialEquations#computeDerivatives} 99 * method).</p> 100 */ 101 int RESET_DERIVATIVES = 2; 102 103 /** Continue indicator. 104 * <p>This value should be used as the return value of the {@link 105 * #eventOccurred eventOccurred} method when the integration should go 106 * on after the event ending the current step.</p> 107 */ 108 int CONTINUE = 3; 109 110 /** Compute the value of the switching function. 111 112 * <p>The discrete events are generated when the sign of this 113 * switching function changes. The integrator will take care to change 114 * the stepsize in such a way these events occur exactly at step boundaries. 115 * The switching function must be continuous in its roots neighborhood 116 * (but not necessarily smooth), as the integrator will need to find its 117 * roots to locate precisely the events.</p> 118 119 * @param t current value of the independent <i>time</i> variable 120 * @param y array containing the current value of the state vector 121 * @param dydy0 array containing the current value of the jacobian of 122 * the state vector with respect to initial state 123 * @param dydp array containing the current value of the jacobian of 124 * the state vector with respect to parameters 125 * @return value of the g switching function 126 * @exception EventException if the switching function cannot be evaluated 127 */ g(double t, double[] y, double[][] dydy0, double[][] dydp)128 double g(double t, double[] y, double[][] dydy0, double[][] dydp) 129 throws EventException; 130 131 /** Handle an event and choose what to do next. 132 133 * <p>This method is called when the integrator has accepted a step 134 * ending exactly on a sign change of the function, just <em>before</em> 135 * the step handler itself is called (see below for scheduling). It 136 * allows the user to update his internal data to acknowledge the fact 137 * the event has been handled (for example setting a flag in the {@link 138 * org.apache.commons.math.ode.jacobians.ODEWithJacobians 139 * differential equations} to switch the derivatives computation in 140 * case of discontinuity), or to direct the integrator to either stop 141 * or continue integration, possibly with a reset state or derivatives.</p> 142 143 * <ul> 144 * <li>if {@link #STOP} is returned, the step handler will be called 145 * with the <code>isLast</code> flag of the {@link 146 * org.apache.commons.math.ode.jacobians.StepHandlerWithJacobians#handleStep( 147 * StepInterpolatorWithJacobians, boolean) handleStep} method set to true and 148 * the integration will be stopped,</li> 149 * <li>if {@link #RESET_STATE} is returned, the {@link #resetState 150 * resetState} method will be called once the step handler has 151 * finished its task, and the integrator will also recompute the 152 * derivatives,</li> 153 * <li>if {@link #RESET_DERIVATIVES} is returned, the integrator 154 * will recompute the derivatives, 155 * <li>if {@link #CONTINUE} is returned, no specific action will 156 * be taken (apart from having called this method) and integration 157 * will continue.</li> 158 * </ul> 159 160 * <p>The scheduling between this method and the {@link 161 * org.apache.commons.math.ode.jacobians.StepHandlerWithJacobians 162 * StepHandlerWithJacobians} method {@link 163 * org.apache.commons.math.ode.jacobians.StepHandlerWithJacobians#handleStep( 164 * StepInterpolatorWithJacobians, boolean) handleStep(interpolator, isLast)} 165 * is to call this method first and <code>handleStep</code> afterwards. This 166 * scheduling allows the integrator to pass <code>true</code> as the 167 * <code>isLast</code> parameter to the step handler to make it aware the step 168 * will be the last one if this method returns {@link #STOP}. As the 169 * interpolator may be used to navigate back throughout the last step (as {@link 170 * org.apache.commons.math.ode.sampling.StepNormalizer StepNormalizer} 171 * does for example), user code called by this method and user 172 * code called by step handlers may experience apparently out of order values 173 * of the independent time variable. As an example, if the same user object 174 * implements both this {@link EventHandlerWithJacobians EventHandler} interface and the 175 * {@link org.apache.commons.math.ode.sampling.FixedStepHandler FixedStepHandler} 176 * interface, a <em>forward</em> integration may call its 177 * <code>eventOccurred</code> method with t = 10 first and call its 178 * <code>handleStep</code> method with t = 9 afterwards. Such out of order 179 * calls are limited to the size of the integration step for {@link 180 * org.apache.commons.math.ode.sampling.StepHandler variable step handlers} and 181 * to the size of the fixed step for {@link 182 * org.apache.commons.math.ode.sampling.FixedStepHandler fixed step handlers}.</p> 183 184 * @param t current value of the independent <i>time</i> variable 185 * @param y array containing the current value of the state vector 186 * @param dydy0 array containing the current value of the jacobian of 187 * the state vector with respect to initial state 188 * @param dydp array containing the current value of the jacobian of 189 * the state vector with respect to parameters 190 * @param increasing if true, the value of the switching function increases 191 * when times increases around event (note that increase is measured with respect 192 * to physical time, not with respect to integration which may go backward in time) 193 * @return indication of what the integrator should do next, this 194 * value must be one of {@link #STOP}, {@link #RESET_STATE}, 195 * {@link #RESET_DERIVATIVES} or {@link #CONTINUE} 196 * @exception EventException if the event occurrence triggers an error 197 */ eventOccurred(double t, double[] y, double[][] dydy0, double[][] dydp, boolean increasing)198 int eventOccurred(double t, double[] y, double[][] dydy0, double[][] dydp, 199 boolean increasing) throws EventException; 200 201 /** Reset the state prior to continue the integration. 202 203 * <p>This method is called after the step handler has returned and 204 * before the next step is started, but only when {@link 205 * #eventOccurred} has itself returned the {@link #RESET_STATE} 206 * indicator. It allows the user to reset the state vector for the 207 * next step, without perturbing the step handler of the finishing 208 * step. If the {@link #eventOccurred} never returns the {@link 209 * #RESET_STATE} indicator, this function will never be called, and it is 210 * safe to leave its body empty.</p> 211 212 * @param t current value of the independent <i>time</i> variable 213 * @param y array containing the current value of the state vector 214 * the new state should be put in the same array 215 * @param dydy0 array containing the current value of the jacobian of 216 * the state vector with respect to initial state, the new jacobian 217 * should be put in the same array 218 * @param dydp array containing the current value of the jacobian of 219 * the state vector with respect to parameters, the new jacobian 220 * should be put in the same array 221 * @exception EventException if the state cannot be reseted 222 */ resetState(double t, double[] y, double[][] dydy0, double[][] dydp)223 void resetState(double t, double[] y, double[][] dydy0, double[][] dydp) 224 throws EventException; 225 226 } 227