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1   /*
2    * Licensed to the Hipparchus project 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 Hipparchus project 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    *      https://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.hipparchus.ode;
19  
20  
21  /** This interface represents a second order differential equations set.
22  
23   * <p>This interface should be implemented by all real second order
24   * differential equation problems before they can be handled by the
25   * integrators {@link FirstOrderConverter converter to first order}.</p>
26   *
27   * <p>A second order differential equations problem, as seen by an
28   * integrator is the second time derivative <code>d2Y/dt^2</code> of a
29   * state vector <code>Y</code>, both being one dimensional
30   * arrays. From the integrator point of view, this derivative depends
31   * only on the current time <code>t</code>, on the state vector
32   * <code>Y</code> and on the first time derivative of the state
33   * vector.</p>
34   *
35   * <p>For real problems, the derivative depends also on parameters
36   * that do not belong to the state vector (dynamical model constants
37   * for example). These constants are completely outside of the scope
38   * of this interface, the classes that implement it are allowed to
39   * handle them as they want.</p>
40   *
41   * @see FirstOrderConverter
42   * @see OrdinaryDifferentialEquation
43   */
44  
45  public interface SecondOrderODE {
46  
47      /** Get the dimension of the problem.
48       * @return dimension of the problem
49       */
50      int getDimension();
51  
52      /** Get the current time derivative of the state vector.
53       * @param t current value of the independent <I>time</I> variable
54       * @param y array containing the current value of the state vector
55       * @param yDot array containing the current value of the first derivative
56       * of the state vector
57       * @return second time derivative of the state vector
58       */
59      double[] computeSecondDerivatives(double t, double[] y, double[] yDot);
60  
61  }