    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;
    019
    020
    021    /** This interface represents a second order differential equations set.
    022
    023     * <p>This interface should be implemented by all real second order
    024     * differential equation problems before they can be handled by the
    025     * integrators {@link SecondOrderIntegrator#integrate} method.</p>
    026     *
    027     * <p>A second order differential equations problem, as seen by an
    028     * integrator is the second time derivative <code>d2Y/dt^2</code> of a
    029     * state vector <code>Y</code>, both being one dimensional
    030     * arrays. From the integrator point of view, this derivative depends
    031     * only on the current time <code>t</code>, on the state vector
    032     * <code>Y</code> and on the first time derivative of the state
    033     * vector.</p>
    034     *
    035     * <p>For real problems, the derivative depends also on parameters
    036     * that do not belong to the state vector (dynamical model constants
    037     * for example). These constants are completely outside of the scope
    038     * of this interface, the classes that implement it are allowed to
    039     * handle them as they want.</p>
    040     *
    041     * @see SecondOrderIntegrator
    042     * @see FirstOrderConverter
    043     * @see FirstOrderDifferentialEquations
    044     * @version $Id: SecondOrderDifferentialEquations.java 1416643 2012-12-03 19:37:14Z tn $
    045     * @since 1.2
    046     */
    047
    048    public interface SecondOrderDifferentialEquations {
    049
    050        /** Get the dimension of the problem.
    051         * @return dimension of the problem
    052         */
    053        int getDimension();
    054
    055        /** Get the current time derivative of the state vector.
    056         * @param t current value of the independent <I>time</I> variable
    057         * @param y array containing the current value of the state vector
    058         * @param yDot array containing the current value of the first derivative
    059         * of the state vector
    060         * @param yDDot placeholder array where to put the second time derivative
    061         * of the state vector
    062         */
    063        void computeSecondDerivatives(double t, double[] y, double[] yDot, double[] yDDot);
    064
    065    }