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
018 package org.apache.commons.math.ode.nonstiff;
019
020
021 /**
022 * This class implements a second order Runge-Kutta integrator for
023 * Ordinary Differential Equations.
024 *
025 * <p>This method is an explicit Runge-Kutta method, its Butcher-array
026 * is the following one :
027 * <pre>
028 * 0 | 0 0
029 * 1/2 | 1/2 0
030 * |----------
031 * | 0 1
032 * </pre>
033 * </p>
034 *
035 * @see EulerIntegrator
036 * @see ClassicalRungeKuttaIntegrator
037 * @see GillIntegrator
038 *
039 * @version $Revision: 810196 $ $Date: 2009-09-01 15:47:46 -0400 (Tue, 01 Sep 2009) $
040 * @since 1.2
041 */
042
043 public class MidpointIntegrator extends RungeKuttaIntegrator {
044
045 /** Time steps Butcher array. */
046 private static final double[] STATIC_C = {
047 1.0 / 2.0
048 };
049
050 /** Internal weights Butcher array. */
051 private static final double[][] STATIC_A = {
052 { 1.0 / 2.0 }
053 };
054
055 /** Propagation weights Butcher array. */
056 private static final double[] STATIC_B = {
057 0.0, 1.0
058 };
059
060 /** Simple constructor.
061 * Build a midpoint integrator with the given step.
062 * @param step integration step
063 */
064 public MidpointIntegrator(final double step) {
065 super("midpoint", STATIC_C, STATIC_A, STATIC_B, new MidpointStepInterpolator(), step);
066 }
067
068 }