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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package org.apache.commons.math.ode;
19  
20  /** This interface represents a second order differential equations set.
21  
22   * <p>This interface should be implemented by all real second order
23   * differential equation problems before they can be handled by the
24   * integrators {@link SecondOrderIntegrator#integrate} method.</p>
25   *
26   * <p>A second order differential equations problem, as seen by an
27   * integrator is the second time derivative <code>d2Y/dt^2</code> of a
28   * state vector <code>Y</code>, both being one dimensional
29   * arrays. From the integrator point of view, this derivative depends
30   * only on the current time <code>t</code>, on the state vector
31   * <code>Y</code> and on the first time derivative of the state
32   * vector.</p>
33   *
34   * <p>For real problems, the derivative depends also on parameters
35   * that do not belong to the state vector (dynamical model constants
36   * for example). These constants are completely outside of the scope
37   * of this interface, the classes that implement it are allowed to
38   * handle them as they want.</p>
39   *
40   * @see SecondOrderIntegrator
41   * @see FirstOrderConverter
42   * @see FirstOrderDifferentialEquations
43   * @version $Revision: 786927 $ $Date: 2009-06-20 19:37:47 -0400 (Sat, 20 Jun 2009) $
44   * @since 1.2
45   */
46  
47  public interface SecondOrderDifferentialEquations {
48  
49    /** Get the dimension of the problem.
50     * @return dimension of the problem
51     */
52    public int getDimension();
53      
54    /** Get the current time derivative of the state vector.
55     * @param t current value of the independent <I>time</I> variable
56     * @param y array containing the current value of the state vector
57     * @param yDot array containing the current value of the first derivative
58     * of the state vector
59     * @param yDDot placeholder array where to put the second time derivative
60     * of the state vector
61     * @throws DerivativeException this exception is propagated to the caller if the
62     * underlying user function triggers one
63     */
64    public void computeSecondDerivatives(double t, double[] y, double[] yDot,
65                                         double[] yDDot)
66    throws DerivativeException;
67  
68  }