001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018 package org.apache.commons.math.ode.jacobians;
019
020 import org.apache.commons.math.ode.events.EventException;
021
022 /** This interface represents a handler for discrete events triggered
023 * during ODE integration.
024 *
025 * <p>Some events can be triggered at discrete times as an ODE problem
026 * is solved. This occurs for example when the integration process
027 * should be stopped as some state is reached (G-stop facility) when the
028 * precise date is unknown a priori, or when the derivatives have
029 * discontinuities, or simply when the user wants to monitor some
030 * states boundaries crossings.
031 * </p>
032 *
033 * <p>These events are defined as occurring when a <code>g</code>
034 * switching function sign changes.</p>
035 *
036 * <p>Since events are only problem-dependent and are triggered by the
037 * independent <i>time</i> variable and the state vector, they can
038 * occur at virtually any time, unknown in advance. The integrators will
039 * take care to avoid sign changes inside the steps, they will reduce
040 * the step size when such an event is detected in order to put this
041 * event exactly at the end of the current step. This guarantees that
042 * step interpolation (which always has a one step scope) is relevant
043 * even in presence of discontinuities. This is independent from the
044 * stepsize control provided by integrators that monitor the local
045 * error (this event handling feature is available for all integrators,
046 * including fixed step ones).</p>
047 *
048 * <p>Note that is is possible to register a {@link
049 * org.apache.commons.math.ode.events.EventHandler classical event handler}
050 * in the low level integrator used to build a {@link FirstOrderIntegratorWithJacobians}
051 * rather than implementing this class. The event handlers registered at low level
052 * will see the big compound state whether the event handlers defined by this interface
053 * see the original state, and its jacobians in separate arrays.</p>
054 *
055 * <p>The compound state is guaranteed to contain the original state in the first
056 * elements, followed by the jacobian with respect to initial state (in row order),
057 * followed by the jacobian with respect to parameters (in row order). If for example
058 * the original state dimension is 6 and there are 3 parameters, the compound state will
059 * be a 60 elements array. The first 6 elements will be the original state, the next 36
060 * elements will be the jacobian with respect to initial state, and the remaining 18 elements
061 * will be the jacobian with respect to parameters.</p>
062 *
063 * <p>Dealing with low level event handlers is cumbersome if one really needs the jacobians
064 * in these methods, but it also prevents many data being copied back and forth between
065 * state and jacobians on one side and compound state on the other side. So for performance
066 * reasons, it is recommended to use this interface <em>only</em> if jacobians are really
067 * needed and to use lower level handlers if only state is needed.</p>
068 *
069 * @version $Revision: 1037341 $ $Date: 2010-11-20 22:58:35 +0100 (sam. 20 nov. 2010) $
070 * @since 2.1
071 * @deprecated as of 2.2 the complete package is deprecated, it will be replaced
072 * in 3.0 by a completely rewritten implementation
073 */
074 @Deprecated
075 public interface EventHandlerWithJacobians {
076
077 /** Stop indicator.
078 * <p>This value should be used as the return value of the {@link
079 * #eventOccurred eventOccurred} method when the integration should be
080 * stopped after the event ending the current step.</p>
081 */
082 int STOP = 0;
083
084 /** Reset state indicator.
085 * <p>This value should be used as the return value of the {@link
086 * #eventOccurred eventOccurred} method when the integration should
087 * go on after the event ending the current step, with a new state
088 * vector (which will be retrieved thanks to the {@link #resetState
089 * resetState} method).</p>
090 */
091 int RESET_STATE = 1;
092
093 /** Reset derivatives indicator.
094 * <p>This value should be used as the return value of the {@link
095 * #eventOccurred eventOccurred} method when the integration should
096 * go on after the event ending the current step, with a new derivatives
097 * vector (which will be retrieved thanks to the {@link
098 * org.apache.commons.math.ode.FirstOrderDifferentialEquations#computeDerivatives}
099 * 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 */
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 */
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 */
223 void resetState(double t, double[] y, double[][] dydy0, double[][] dydp)
224 throws EventException;
225
226 }