    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    }