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.math.ode;
019    
020    /** This interface represents a second order differential equations set.
021    
022     * <p>This interface should be implemented by all real second order
023     * differential equation problems before they can be handled by the
024     * integrators {@link SecondOrderIntegrator#integrate} method.</p>
025     *
026     * <p>A second order differential equations problem, as seen by an
027     * integrator is the second time derivative <code>d2Y/dt^2</code> of a
028     * state vector <code>Y</code>, both being one dimensional
029     * arrays. From the integrator point of view, this derivative depends
030     * only on the current time <code>t</code>, on the state vector
031     * <code>Y</code> and on the first time derivative of the state
032     * vector.</p>
033     *
034     * <p>For real problems, the derivative depends also on parameters
035     * that do not belong to the state vector (dynamical model constants
036     * for example). These constants are completely outside of the scope
037     * of this interface, the classes that implement it are allowed to
038     * handle them as they want.</p>
039     *
040     * @see SecondOrderIntegrator
041     * @see FirstOrderConverter
042     * @see FirstOrderDifferentialEquations
043     * @version $Revision: 811786 $ $Date: 2009-09-06 05:36:08 -0400 (Sun, 06 Sep 2009) $
044     * @since 1.2
045     */
046    
047    public 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         * @throws DerivativeException this exception is propagated to the caller if the
062         * underlying user function triggers one
063         */
064        void computeSecondDerivatives(double t, double[] y, double[] yDot,
065                                      double[] yDDot) throws DerivativeException;
066    
067    }