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 020import org.apache.commons.math3.Field; 021import org.apache.commons.math3.RealFieldElement; 022import org.apache.commons.math3.ode.FieldEquationsMapper; 023import org.apache.commons.math3.ode.FieldODEStateAndDerivative; 024import org.apache.commons.math3.util.MathArrays; 025 026/** 027 * This class implements the 3/8 fourth order Runge-Kutta 028 * integrator for Ordinary Differential Equations. 029 * 030 * <p>This method is an explicit Runge-Kutta method, its Butcher-array 031 * is the following one : 032 * <pre> 033 * 0 | 0 0 0 0 034 * 1/3 | 1/3 0 0 0 035 * 2/3 |-1/3 1 0 0 036 * 1 | 1 -1 1 0 037 * |-------------------- 038 * | 1/8 3/8 3/8 1/8 039 * </pre> 040 * </p> 041 * 042 * @see EulerFieldIntegrator 043 * @see ClassicalRungeKuttaFieldIntegrator 044 * @see GillFieldIntegrator 045 * @see MidpointFieldIntegrator 046 * @see LutherFieldIntegrator 047 * @param <T> the type of the field elements 048 * @since 3.6 049 */ 050 051public class ThreeEighthesFieldIntegrator<T extends RealFieldElement<T>> 052 extends RungeKuttaFieldIntegrator<T> { 053 054 /** Simple constructor. 055 * Build a 3/8 integrator with the given step. 056 * @param field field to which the time and state vector elements belong 057 * @param step integration step 058 */ 059 public ThreeEighthesFieldIntegrator(final Field<T> field, final T step) { 060 super(field, "3/8", step); 061 } 062 063 /** {@inheritDoc} */ 064 public T[] getC() { 065 final T[] c = MathArrays.buildArray(getField(), 3); 066 c[0] = fraction(1, 3); 067 c[1] = c[0].add(c[0]); 068 c[2] = getField().getOne(); 069 return c; 070 } 071 072 /** {@inheritDoc} */ 073 public T[][] getA() { 074 final T[][] a = MathArrays.buildArray(getField(), 3, -1); 075 for (int i = 0; i < a.length; ++i) { 076 a[i] = MathArrays.buildArray(getField(), i + 1); 077 } 078 a[0][0] = fraction(1, 3); 079 a[1][0] = a[0][0].negate(); 080 a[1][1] = getField().getOne(); 081 a[2][0] = getField().getOne(); 082 a[2][1] = getField().getOne().negate(); 083 a[2][2] = getField().getOne(); 084 return a; 085 } 086 087 /** {@inheritDoc} */ 088 public T[] getB() { 089 final T[] b = MathArrays.buildArray(getField(), 4); 090 b[0] = fraction(1, 8); 091 b[1] = fraction(3, 8); 092 b[2] = b[1]; 093 b[3] = b[0]; 094 return b; 095 } 096 097 /** {@inheritDoc} */ 098 @Override 099 protected ThreeEighthesFieldStepInterpolator<T> 100 createInterpolator(final boolean forward, T[][] yDotK, 101 final FieldODEStateAndDerivative<T> globalPreviousState, 102 final FieldODEStateAndDerivative<T> globalCurrentState, 103 final FieldEquationsMapper<T> mapper) { 104 return new ThreeEighthesFieldStepInterpolator<T>(getField(), forward, yDotK, 105 globalPreviousState, globalCurrentState, 106 globalPreviousState, globalCurrentState, 107 mapper); 108 } 109 110}