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 a second order Runge-Kutta integrator for 028 * 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 0 034 * 1/2 | 1/2 0 035 * |---------- 036 * | 0 1 037 * </pre> 038 * 039 * @see EulerFieldIntegrator 040 * @see ClassicalRungeKuttaFieldIntegrator 041 * @see GillFieldIntegrator 042 * @see ThreeEighthesFieldIntegrator 043 * @see LutherFieldIntegrator 044 * 045 * @param <T> the type of the field elements 046 * @since 3.6 047 */ 048 049public class MidpointFieldIntegrator<T extends RealFieldElement<T>> extends RungeKuttaFieldIntegrator<T> { 050 051 /** Simple constructor. 052 * Build a midpoint integrator with the given step. 053 * @param field field to which the time and state vector elements belong 054 * @param step integration step 055 */ 056 public MidpointFieldIntegrator(final Field<T> field, final T step) { 057 super(field, "midpoint", step); 058 } 059 060 /** {@inheritDoc} */ 061 @Override 062 public T[] getC() { 063 final T[] c = MathArrays.buildArray(getField(), 1); 064 c[0] = getField().getOne().multiply(0.5); 065 return c; 066 } 067 068 /** {@inheritDoc} */ 069 @Override 070 public T[][] getA() { 071 final T[][] a = MathArrays.buildArray(getField(), 1, 1); 072 a[0][0] = fraction(1, 2); 073 return a; 074 } 075 076 /** {@inheritDoc} */ 077 @Override 078 public T[] getB() { 079 final T[] b = MathArrays.buildArray(getField(), 2); 080 b[0] = getField().getZero(); 081 b[1] = getField().getOne(); 082 return b; 083 } 084 085 /** {@inheritDoc} */ 086 @Override 087 protected MidpointFieldStepInterpolator<T> 088 createInterpolator(final boolean forward, T[][] yDotK, 089 final FieldODEStateAndDerivative<T> globalPreviousState, 090 final FieldODEStateAndDerivative<T> globalCurrentState, 091 final FieldEquationsMapper<T> mapper) { 092 return new MidpointFieldStepInterpolator<>(getField(), forward, yDotK, 093 globalPreviousState, globalCurrentState, 094 globalPreviousState, globalCurrentState, 095 mapper); 096 } 097}