1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 18 package org.apache.commons.math.ode.nonstiff; 19 20 21 /** 22 * This class implements the 3/8 fourth order Runge-Kutta 23 * integrator for Ordinary Differential Equations. 24 * 25 * <p>This method is an explicit Runge-Kutta method, its Butcher-array 26 * is the following one : 27 * <pre> 28 * 0 | 0 0 0 0 29 * 1/3 | 1/3 0 0 0 30 * 2/3 |-1/3 1 0 0 31 * 1 | 1 -1 1 0 32 * |-------------------- 33 * | 1/8 3/8 3/8 1/8 34 * </pre> 35 * </p> 36 * 37 * @see EulerIntegrator 38 * @see ClassicalRungeKuttaIntegrator 39 * @see GillIntegrator 40 * @see MidpointIntegrator 41 * @version $Revision: 810196 $ $Date: 2009-09-01 21:47:46 +0200 (mar. 01 sept. 2009) $ 42 * @since 1.2 43 */ 44 45 public class ThreeEighthesIntegrator extends RungeKuttaIntegrator { 46 47 /** Time steps Butcher array. */ 48 private static final double[] STATIC_C = { 49 1.0 / 3.0, 2.0 / 3.0, 1.0 50 }; 51 52 /** Internal weights Butcher array. */ 53 private static final double[][] STATIC_A = { 54 { 1.0 / 3.0 }, 55 { -1.0 / 3.0, 1.0 }, 56 { 1.0, -1.0, 1.0 } 57 }; 58 59 /** Propagation weights Butcher array. */ 60 private static final double[] STATIC_B = { 61 1.0 / 8.0, 3.0 / 8.0, 3.0 / 8.0, 1.0 / 8.0 62 }; 63 64 /** Simple constructor. 65 * Build a 3/8 integrator with the given step. 66 * @param step integration step 67 */ 68 public ThreeEighthesIntegrator(final double step) { 69 super("3/8", STATIC_C, STATIC_A, STATIC_B, new ThreeEighthesStepInterpolator(), step); 70 } 71 72 } 73
