    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.nonstiff;
    019
    020
    021    /**
    022     * This class implements the classical fourth order Runge-Kutta
    023     * integrator for Ordinary Differential Equations (it is the most
    024     * often used Runge-Kutta method).
    025     *
    026     * <p>This method is an explicit Runge-Kutta method, its Butcher-array
    027     * is the following one :
    028     * <pre>
    029     *    0  |  0    0    0    0
    030     *   1/2 | 1/2   0    0    0
    031     *   1/2 |  0   1/2   0    0
    032     *    1  |  0    0    1    0
    033     *       |--------------------
    034     *       | 1/6  1/3  1/3  1/6
    035     * </pre>
    036     * </p>
    037     *
    038     * @see EulerIntegrator
    039     * @see GillIntegrator
    040     * @see MidpointIntegrator
    041     * @see ThreeEighthesIntegrator
    042     * @version $Id: ClassicalRungeKuttaIntegrator.java 1416643 2012-12-03 19:37:14Z tn $
    043     * @since 1.2
    044     */
    045
    046    public class ClassicalRungeKuttaIntegrator extends RungeKuttaIntegrator {
    047
    048      /** Time steps Butcher array. */
    049      private static final double[] STATIC_C = {
    050        1.0 / 2.0, 1.0 / 2.0, 1.0
    051      };
    052
    053      /** Internal weights Butcher array. */
    054      private static final double[][] STATIC_A = {
    055        { 1.0 / 2.0 },
    056        { 0.0, 1.0 / 2.0 },
    057        { 0.0, 0.0, 1.0 }
    058      };
    059
    060      /** Propagation weights Butcher array. */
    061      private static final double[] STATIC_B = {
    062        1.0 / 6.0, 1.0 / 3.0, 1.0 / 3.0, 1.0 / 6.0
    063      };
    064
    065      /** Simple constructor.
    066       * Build a fourth-order Runge-Kutta integrator with the given
    067       * step.
    068       * @param step integration step
    069       */
    070      public ClassicalRungeKuttaIntegrator(final double step) {
    071        super("classical Runge-Kutta", STATIC_C, STATIC_A, STATIC_B,
    072              new ClassicalRungeKuttaStepInterpolator(), step);
    073      }
    074
    075    }