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.math4.legacy.ode.nonstiff; 019 020import org.apache.commons.math4.legacy.core.Field; 021import org.apache.commons.math4.legacy.core.RealFieldElement; 022import org.apache.commons.math4.legacy.ode.FieldEquationsMapper; 023import org.apache.commons.math4.legacy.ode.FieldODEStateAndDerivative; 024import org.apache.commons.math4.legacy.core.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 * 041 * @see EulerFieldIntegrator 042 * @see ClassicalRungeKuttaFieldIntegrator 043 * @see GillFieldIntegrator 044 * @see MidpointFieldIntegrator 045 * @see LutherFieldIntegrator 046 * @param <T> the type of the field elements 047 * @since 3.6 048 */ 049 050public class ThreeEighthesFieldIntegrator<T extends RealFieldElement<T>> 051 extends RungeKuttaFieldIntegrator<T> { 052 053 /** Simple constructor. 054 * Build a 3/8 integrator with the given step. 055 * @param field field to which the time and state vector elements belong 056 * @param step integration step 057 */ 058 public ThreeEighthesFieldIntegrator(final Field<T> field, final T step) { 059 super(field, "3/8", step); 060 } 061 062 /** {@inheritDoc} */ 063 @Override 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 @Override 074 public T[][] getA() { 075 final T[][] a = MathArrays.buildArray(getField(), 3, -1); 076 for (int i = 0; i < a.length; ++i) { 077 a[i] = MathArrays.buildArray(getField(), i + 1); 078 } 079 a[0][0] = fraction(1, 3); 080 a[1][0] = a[0][0].negate(); 081 a[1][1] = getField().getOne(); 082 a[2][0] = getField().getOne(); 083 a[2][1] = getField().getOne().negate(); 084 a[2][2] = getField().getOne(); 085 return a; 086 } 087 088 /** {@inheritDoc} */ 089 @Override 090 public T[] getB() { 091 final T[] b = MathArrays.buildArray(getField(), 4); 092 b[0] = fraction(1, 8); 093 b[1] = fraction(3, 8); 094 b[2] = b[1]; 095 b[3] = b[0]; 096 return b; 097 } 098 099 /** {@inheritDoc} */ 100 @Override 101 protected ThreeEighthesFieldStepInterpolator<T> 102 createInterpolator(final boolean forward, T[][] yDotK, 103 final FieldODEStateAndDerivative<T> globalPreviousState, 104 final FieldODEStateAndDerivative<T> globalCurrentState, 105 final FieldEquationsMapper<T> mapper) { 106 return new ThreeEighthesFieldStepInterpolator<>(getField(), forward, yDotK, 107 globalPreviousState, globalCurrentState, 108 globalPreviousState, globalCurrentState, 109 mapper); 110 } 111}