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    }