| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package org.apache.commons.math4.legacy.ode.nonstiff; |
| |
| import org.apache.commons.math4.legacy.core.Field; |
| import org.apache.commons.math4.legacy.core.RealFieldElement; |
| import org.apache.commons.math4.legacy.ode.FieldEquationsMapper; |
| import org.apache.commons.math4.legacy.ode.FieldODEStateAndDerivative; |
| import org.apache.commons.math4.legacy.core.MathArrays; |
| |
| /** |
| * This class implements a second order Runge-Kutta integrator for |
| * Ordinary Differential Equations. |
| * |
| * <p>This method is an explicit Runge-Kutta method, its Butcher-array |
| * is the following one : |
| * <pre> |
| * 0 | 0 0 |
| * 1/2 | 1/2 0 |
| * |---------- |
| * | 0 1 |
| * </pre> |
| * |
| * @see EulerFieldIntegrator |
| * @see ClassicalRungeKuttaFieldIntegrator |
| * @see GillFieldIntegrator |
| * @see ThreeEighthesFieldIntegrator |
| * @see LutherFieldIntegrator |
| * |
| * @param <T> the type of the field elements |
| * @since 3.6 |
| */ |
| |
| public class MidpointFieldIntegrator<T extends RealFieldElement<T>> extends RungeKuttaFieldIntegrator<T> { |
| |
| /** Simple constructor. |
| * Build a midpoint integrator with the given step. |
| * @param field field to which the time and state vector elements belong |
| * @param step integration step |
| */ |
| public MidpointFieldIntegrator(final Field<T> field, final T step) { |
| super(field, "midpoint", step); |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public T[] getC() { |
| final T[] c = MathArrays.buildArray(getField(), 1); |
| c[0] = getField().getOne().multiply(0.5); |
| return c; |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public T[][] getA() { |
| final T[][] a = MathArrays.buildArray(getField(), 1, 1); |
| a[0][0] = fraction(1, 2); |
| return a; |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public T[] getB() { |
| final T[] b = MathArrays.buildArray(getField(), 2); |
| b[0] = getField().getZero(); |
| b[1] = getField().getOne(); |
| return b; |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| protected MidpointFieldStepInterpolator<T> |
| createInterpolator(final boolean forward, T[][] yDotK, |
| final FieldODEStateAndDerivative<T> globalPreviousState, |
| final FieldODEStateAndDerivative<T> globalCurrentState, |
| final FieldEquationsMapper<T> mapper) { |
| return new MidpointFieldStepInterpolator<>(getField(), forward, yDotK, |
| globalPreviousState, globalCurrentState, |
| globalPreviousState, globalCurrentState, |
| mapper); |
| } |
| |
| } |