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 classical fourth order Runge-Kutta 028 * integrator for Ordinary Differential Equations (it is the most 029 * often used Runge-Kutta method). 030 * 031 * <p>This method is an explicit Runge-Kutta method, its Butcher-array 032 * is the following one : 033 * <pre> 034 * 0 | 0 0 0 0 035 * 1/2 | 1/2 0 0 0 036 * 1/2 | 0 1/2 0 0 037 * 1 | 0 0 1 0 038 * |-------------------- 039 * | 1/6 1/3 1/3 1/6 040 * </pre> 041 * 042 * @see EulerFieldIntegrator 043 * @see GillFieldIntegrator 044 * @see MidpointFieldIntegrator 045 * @see ThreeEighthesFieldIntegrator 046 * @see LutherFieldIntegrator 047 * @param <T> the type of the field elements 048 * @since 3.6 049 */ 050 051public class ClassicalRungeKuttaFieldIntegrator<T extends RealFieldElement<T>> 052 extends RungeKuttaFieldIntegrator<T> { 053 054 /** Simple constructor. 055 * Build a fourth-order Runge-Kutta 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 ClassicalRungeKuttaFieldIntegrator(final Field<T> field, final T step) { 060 super(field, "classical Runge-Kutta", step); 061 } 062 063 /** {@inheritDoc} */ 064 @Override 065 public T[] getC() { 066 final T[] c = MathArrays.buildArray(getField(), 3); 067 c[0] = getField().getOne().multiply(0.5); 068 c[1] = c[0]; 069 c[2] = getField().getOne(); 070 return c; 071 } 072 073 /** {@inheritDoc} */ 074 @Override 075 public T[][] getA() { 076 final T[][] a = MathArrays.buildArray(getField(), 3, -1); 077 for (int i = 0; i < a.length; ++i) { 078 a[i] = MathArrays.buildArray(getField(), i + 1); 079 } 080 a[0][0] = fraction(1, 2); 081 a[1][0] = getField().getZero(); 082 a[1][1] = a[0][0]; 083 a[2][0] = getField().getZero(); 084 a[2][1] = getField().getZero(); 085 a[2][2] = getField().getOne(); 086 return a; 087 } 088 089 /** {@inheritDoc} */ 090 @Override 091 public T[] getB() { 092 final T[] b = MathArrays.buildArray(getField(), 4); 093 b[0] = fraction(1, 6); 094 b[1] = fraction(1, 3); 095 b[2] = b[1]; 096 b[3] = b[0]; 097 return b; 098 } 099 100 /** {@inheritDoc} */ 101 @Override 102 protected ClassicalRungeKuttaFieldStepInterpolator<T> 103 createInterpolator(final boolean forward, T[][] yDotK, 104 final FieldODEStateAndDerivative<T> globalPreviousState, 105 final FieldODEStateAndDerivative<T> globalCurrentState, 106 final FieldEquationsMapper<T> mapper) { 107 return new ClassicalRungeKuttaFieldStepInterpolator<>(getField(), forward, yDotK, 108 globalPreviousState, globalCurrentState, 109 globalPreviousState, globalCurrentState, 110 mapper); 111 } 112}