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
018package 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 * @since 1.2
045 */
046
047public interface SecondOrderDifferentialEquations {
048
049    /** Get the dimension of the problem.
050     * @return dimension of the problem
051     */
052    int getDimension();
053
054    /** Get the current time derivative of the state vector.
055     * @param t current value of the independent <I>time</I> variable
056     * @param y array containing the current value of the state vector
057     * @param yDot array containing the current value of the first derivative
058     * of the state vector
059     * @param yDDot placeholder array where to put the second time derivative
060     * of the state vector
061     */
062    void computeSecondDerivatives(double t, double[] y, double[] yDot, double[] yDDot);
063
064}