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    }