    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    }