    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    }