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.math3.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 $Id: MidpointIntegrator.java 1416643 2012-12-03 19:37:14Z tn $
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    }