| /* |
| * 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.math3.ode.nonstiff; |
| |
| import org.apache.commons.math3.util.FastMath; |
| |
| |
| /** |
| * This class implements the Gill fourth 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 0 0 |
| * 1/2 | 1/2 0 0 0 |
| * 1/2 | (q-1)/2 (2-q)/2 0 0 |
| * 1 | 0 -q/2 (2+q)/2 0 |
| * |------------------------------- |
| * | 1/6 (2-q)/6 (2+q)/6 1/6 |
| * </pre> |
| * where q = sqrt(2)</p> |
| * |
| * @see EulerIntegrator |
| * @see ClassicalRungeKuttaIntegrator |
| * @see MidpointIntegrator |
| * @see ThreeEighthesIntegrator |
| * @see LutherIntegrator |
| * @since 1.2 |
| */ |
| |
| public class GillIntegrator extends RungeKuttaIntegrator { |
| |
| /** Time steps Butcher array. */ |
| private static final double[] STATIC_C = { |
| 1.0 / 2.0, 1.0 / 2.0, 1.0 |
| }; |
| |
| /** Internal weights Butcher array. */ |
| private static final double[][] STATIC_A = { |
| { 1.0 / 2.0 }, |
| { (FastMath.sqrt(2.0) - 1.0) / 2.0, (2.0 - FastMath.sqrt(2.0)) / 2.0 }, |
| { 0.0, -FastMath.sqrt(2.0) / 2.0, (2.0 + FastMath.sqrt(2.0)) / 2.0 } |
| }; |
| |
| /** Propagation weights Butcher array. */ |
| private static final double[] STATIC_B = { |
| 1.0 / 6.0, (2.0 - FastMath.sqrt(2.0)) / 6.0, (2.0 + FastMath.sqrt(2.0)) / 6.0, 1.0 / 6.0 |
| }; |
| |
| /** Simple constructor. |
| * Build a fourth-order Gill integrator with the given step. |
| * @param step integration step |
| */ |
| public GillIntegrator(final double step) { |
| super("Gill", STATIC_C, STATIC_A, STATIC_B, new GillStepInterpolator(), step); |
| } |
| |
| } |