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
018package org.apache.commons.math3.ode.nonstiff;
019
020
021/**
022 * This class implements the 3/8 fourth order Runge-Kutta
023 * integrator for Ordinary Differential Equations.
024 *
025 * <p>This method is an explicit Runge-Kutta method, its Butcher-array
026 * is the following one :
027 * <pre>
028 *    0  |  0    0    0    0
029 *   1/3 | 1/3   0    0    0
030 *   2/3 |-1/3   1    0    0
031 *    1  |  1   -1    1    0
032 *       |--------------------
033 *       | 1/8  3/8  3/8  1/8
034 * </pre>
035 * </p>
036 *
037 * @see EulerIntegrator
038 * @see ClassicalRungeKuttaIntegrator
039 * @see GillIntegrator
040 * @see MidpointIntegrator
041 * @version $Id: ThreeEighthesIntegrator.java 1416643 2012-12-03 19:37:14Z tn $
042 * @since 1.2
043 */
044
045public class ThreeEighthesIntegrator extends RungeKuttaIntegrator {
046
047  /** Time steps Butcher array. */
048  private static final double[] STATIC_C = {
049    1.0 / 3.0, 2.0 / 3.0, 1.0
050  };
051
052  /** Internal weights Butcher array. */
053  private static final double[][] STATIC_A = {
054    {  1.0 / 3.0 },
055    { -1.0 / 3.0, 1.0 },
056    {  1.0, -1.0, 1.0 }
057  };
058
059  /** Propagation weights Butcher array. */
060  private static final double[] STATIC_B = {
061    1.0 / 8.0, 3.0 / 8.0, 3.0 / 8.0, 1.0 / 8.0
062  };
063
064  /** Simple constructor.
065   * Build a 3/8 integrator with the given step.
066   * @param step integration step
067   */
068  public ThreeEighthesIntegrator(final double step) {
069    super("3/8", STATIC_C, STATIC_A, STATIC_B, new ThreeEighthesStepInterpolator(), step);
070  }
071
072}