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    
021    
022    /** This interface represents a first order differential equations set.
023     *
024     * <p>This interface should be implemented by all real first order
025     * differential equation problems before they can be handled by the
026     * integrators {@link FirstOrderIntegrator#integrate} method.</p>
027     *
028     * <p>A first order differential equations problem, as seen by an
029     * integrator is the time derivative <code>dY/dt</code> of a state
030     * vector <code>Y</code>, both being one dimensional arrays. From the
031     * integrator point of view, this derivative depends only on the
032     * current time <code>t</code> and on the state vector
033     * <code>Y</code>.</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 FirstOrderIntegrator
042     * @see FirstOrderConverter
043     * @see SecondOrderDifferentialEquations
044     *
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 FirstOrderDifferentialEquations {
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 placeholder array where to put the time derivative of the state vector
060         * @throws DerivativeException this user-defined exception should be used if an error is
061         * is triggered by user code
062         */
063        void computeDerivatives(double t, double[] y, double[] yDot)
064            throws DerivativeException;
065    
066    }