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    import org.apache.commons.math.ode.DerivativeException;
021    
022    /** This interface represents a second order differential equations set.
023    
024     * <p>This interface should be implemented by all real second order
025     * differential equation problems before they can be handled by the
026     * integrators {@link SecondOrderIntegrator#integrate} method.</p>
027     *
028     * <p>A second order differential equations problem, as seen by an
029     * integrator is the second time derivative <code>d2Y/dt^2</code> of a
030     * state vector <code>Y</code>, both being one dimensional
031     * arrays. From the integrator point of view, this derivative depends
032     * only on the current time <code>t</code>, on the state vector
033     * <code>Y</code> and on the first time derivative of the state
034     * vector.</p>
035     *
036     * <p>For real problems, the derivative depends also on parameters
037     * that do not belong to the state vector (dynamical model constants
038     * for example). These constants are completely outside of the scope
039     * of this interface, the classes that implement it are allowed to
040     * handle them as they want.</p>
041     *
042     * @see SecondOrderIntegrator
043     * @see FirstOrderConverter
044     * @see FirstOrderDifferentialEquations
045     * @version $Revision: 1073158 $ $Date: 2011-02-21 22:46:52 +0100 (lun. 21 f??vr. 2011) $
046     * @since 1.2
047     */
048    
049    public interface SecondOrderDifferentialEquations {
050    
051        /** Get the dimension of the problem.
052         * @return dimension of the problem
053         */
054        int getDimension();
055    
056        /** Get the current time derivative of the state vector.
057         * @param t current value of the independent <I>time</I> variable
058         * @param y array containing the current value of the state vector
059         * @param yDot array containing the current value of the first derivative
060         * of the state vector
061         * @param yDDot placeholder array where to put the second time derivative
062         * of the state vector
063         * @throws DerivativeException this user-defined exception should be used if an error is
064         * is triggered by user code
065         */
066        void computeSecondDerivatives(double t, double[] y, double[] yDot, double[] yDDot)
067            throws DerivativeException;
068    
069    }