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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  
21  /** This interface represents a first order differential equations set.
22   *
23   * <p>This interface should be implemented by all real first order
24   * differential equation problems before they can be handled by the
25   * integrators {@link FirstOrderIntegrator#integrate} method.</p>
26   *
27   * <p>A first order differential equations problem, as seen by an
28   * integrator is the time derivative <code>dY/dt</code> of a state
29   * vector <code>Y</code>, both being one dimensional arrays. From the
30   * integrator point of view, this derivative depends only on the
31   * current time <code>t</code> and on the state vector
32   * <code>Y</code>.</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 FirstOrderIntegrator
41   * @see FirstOrderConverter
42   * @see SecondOrderDifferentialEquations
43   *
44   * @version $Revision: 786881 $ $Date: 2009-06-20 14:53:08 -0400 (Sat, 20 Jun 2009) $
45   * @since 1.2
46   */
47  
48  public interface FirstOrderDifferentialEquations {
49      
50      /** Get the dimension of the problem.
51       * @return dimension of the problem
52       */
53      public int getDimension();
54      
55      /** Get the current time derivative of the state vector.
56       * @param t current value of the independent <I>time</I> variable
57       * @param y array containing the current value of the state vector
58       * @param yDot placeholder array where to put the time derivative of the state vector
59       * @throws DerivativeException this exception is propagated to the caller if the
60       * underlying user function triggers one
61       */
62      public void computeDerivatives(double t, double[] y, double[] yDot)
63      throws DerivativeException;
64      
65  }