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.math3.ode.sampling;
019    
020    
021    /**
022     * This interface represents a handler that should be called after
023     * each successful fixed step.
024    
025     * <p>This interface should be implemented by anyone who is interested
026     * in getting the solution of an ordinary differential equation at
027     * fixed time steps. Objects implementing this interface should be
028     * wrapped within an instance of {@link StepNormalizer} that itself
029     * is used as the general {@link StepHandler} by the integrator. The
030     * {@link StepNormalizer} object is called according to the integrator
031     * internal algorithms and it calls objects implementing this
032     * interface as necessary at fixed time steps.</p>
033     *
034     * @see StepHandler
035     * @see StepNormalizer
036     * @version $Id: FixedStepHandler.java 1416643 2012-12-03 19:37:14Z tn $
037     * @since 1.2
038     */
039    
040    public interface FixedStepHandler  {
041    
042      /** Initialize step handler at the start of an ODE integration.
043       * <p>
044       * This method is called once at the start of the integration. It
045       * may be used by the step handler to initialize some internal data
046       * if needed.
047       * </p>
048       * @param t0 start value of the independent <i>time</i> variable
049       * @param y0 array containing the start value of the state vector
050       * @param t target time for the integration
051       */
052      void init(double t0, double[] y0, double t);
053    
054      /**
055       * Handle the last accepted step
056       * @param t time of the current step
057       * @param y state vector at t. For efficiency purposes, the {@link
058       * StepNormalizer} class reuses the same array on each call, so if
059       * the instance wants to keep it across all calls (for example to
060       * provide at the end of the integration a complete array of all
061       * steps), it should build a local copy store this copy.
062       * @param yDot derivatives of the state vector state vector at t.
063       * For efficiency purposes, the {@link StepNormalizer} class reuses
064       * the same array on each call, so if
065       * the instance wants to keep it across all calls (for example to
066       * provide at the end of the integration a complete array of all
067       * steps), it should build a local copy store this copy.
068       * @param isLast true if the step is the last one
069       */
070      void handleStep(double t, double[] y, double[] yDot, boolean isLast);
071    
072    }