| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package org.apache.commons.math.ode; |
| |
| import java.io.Serializable; |
| |
| import org.apache.commons.math.FunctionEvaluationException; |
| |
| /** This interface represents a switching function. |
| * |
| * <p>A switching function allows to handle discrete events in |
| * integration problems. These events occur for example when the |
| * integration process should be stopped as some value is reached |
| * (G-stop facility), or when the derivatives have |
| * discontinuities, or simply when the user wants to monitor some |
| * states boundaries crossings. These events are traditionally defined |
| * as occurring when a <code>g</code> function sign changes, hence |
| * the name <em>switching functions</em>.</p> |
| * |
| * <p>Since events are only problem-dependent and are triggered by the |
| * independent <i>time</i> variable and the state vector, they can |
| * occur at virtually any time, unknown in advance. The integrators will |
| * take care to avoid sign changes inside the steps, they will reduce |
| * the step size when such an event is detected in order to put this |
| * event exactly at the end of the current step. This guarantees that |
| * step interpolation (which always has a one step scope) is relevant |
| * even in presence of discontinuities. This is independent from the |
| * stepsize control provided by integrators that monitor the local |
| * error (this feature is available on all integrators, including |
| * fixed step ones).</p> |
| * |
| * @version $Revision$ $Date$ |
| * @since 1.2 |
| */ |
| |
| public interface SwitchingFunction extends Serializable { |
| |
| /** Stop indicator. |
| * <p>This value should be used as the return value of the {@link |
| * #eventOccurred eventOccurred} method when the integration should be |
| * stopped after the event ending the current step.</p> |
| */ |
| public static final int STOP = 0; |
| |
| /** Reset state indicator. |
| * <p>This value should be used as the return value of the {@link |
| * #eventOccurred eventOccurred} method when the integration should |
| * go on after the event ending the current step, with a new state |
| * vector (which will be retrieved thanks to the {@link #resetState |
| * resetState} method).</p> |
| */ |
| public static final int RESET_STATE = 1; |
| |
| /** Reset derivatives indicator. |
| * <p>This value should be used as the return value of the {@link |
| * #eventOccurred eventOccurred} method when the integration should |
| * go on after the event ending the current step, with a new derivatives |
| * vector (which will be retrieved thanks to the {@link |
| * FirstOrderDifferentialEquations#computeDerivatives} method).</p> |
| */ |
| public static final int RESET_DERIVATIVES = 2; |
| |
| /** Continue indicator. |
| * <p>This value should be used as the return value of the {@link |
| * #eventOccurred eventOccurred} method when the integration should go |
| * on after the event ending the current step.</p> |
| */ |
| public static final int CONTINUE = 3; |
| |
| /** Compute the value of the switching function. |
| |
| * <p>Discrete events are generated when the sign of this function |
| * changes, the integrator will take care to change the stepsize in |
| * such a way these events occur exactly at step boundaries. This |
| * function must be continuous (at least in its roots neighborhood), |
| * as the integrator will need to find its roots to locate the events.</p> |
| |
| * @param t current value of the independent <i>time</i> variable |
| * @param y array containing the current value of the state vector |
| * @return value of the g function |
| * @exception FunctionEvaluationException if the value of the function |
| * cannot be evaluated |
| */ |
| public double g(double t, double[] y) throws FunctionEvaluationException; |
| |
| /** Handle an event and choose what to do next. |
| |
| * <p>This method is called when the integrator has accepted a step |
| * ending exactly on a sign change of the function, just before the |
| * step handler itself is called. It allows the user to update his |
| * internal data to acknowledge the fact the event has been handled |
| * (for example setting a flag in the {@link |
| * FirstOrderDifferentialEquations differential equations} to switch |
| * the derivatives computation in case of discontinuity), or to |
| * direct the integrator to either stop or continue integration, |
| * possibly with a reset state or derivatives.</p> |
| |
| * <ul> |
| * <li>if {@link #STOP} is returned, the step handler will be called |
| * with the <code>isLast</code> flag of the {@link |
| * StepHandler#handleStep handleStep} method set to true and the |
| * integration will be stopped,</li> |
| * <li>if {@link #RESET_STATE} is returned, the {@link #resetState |
| * resetState} method will be called once the step handler has |
| * finished its task, and the integrator will also recompute the |
| * derivatives,</li> |
| * <li>if {@link #RESET_DERIVATIVES} is returned, the integrator |
| * will recompute the derivatives, |
| * <li>if {@link #CONTINUE} is returned, no specific action will |
| * be taken (apart from having called this method) and integration |
| * will continue.</li> |
| * </ul> |
| |
| * @param t current value of the independent <i>time</i> variable |
| * @param y array containing the current value of the state vector |
| * @return indication of what the integrator should do next, this |
| * value must be one of {@link #STOP}, {@link #RESET_STATE}, |
| * {@link #RESET_DERIVATIVES} or {@link #CONTINUE} |
| */ |
| public int eventOccurred(double t, double[] y); |
| |
| /** Reset the state prior to continue the integration. |
| |
| * <p>This method is called after the step handler has returned and |
| * before the next step is started, but only when {@link |
| * #eventOccurred} has itself returned the {@link #RESET_STATE} |
| * indicator. It allows the user to reset the state vector for the |
| * next step, without perturbing the step handler of the finishing |
| * step. If the {@link #eventOccurred} never returns the {@link |
| * #RESET_STATE} indicator, this function will never be called, and it is |
| * safe to leave its body empty.</p> |
| |
| * @param t current value of the independent <i>time</i> variable |
| * @param y array containing the current value of the state vector |
| * the new state should be put in the same array |
| */ |
| public void resetState(double t, double[] y); |
| |
| } |