View Javadoc
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    *      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  /*
19   * This is not the original file distributed by the Apache Software Foundation
20   * It has been modified by the Hipparchus project
21   */
22  
23  package org.hipparchus.ode;
24  
25  import org.hipparchus.CalculusFieldElement;
26  
27  /** This interface represents a first order differential equations set.
28   *
29   * <p>This interface should be implemented by all real first order
30   * differential equation problems before they can be handled by the
31   * integrators {@link FieldODEIntegrator#integrate(FieldExpandableODE,
32   * FieldODEState, CalculusFieldElement)} method.</p>
33   *
34   * <p>A first order differential equations problem, as seen by an
35   * integrator is the time derivative <code>dY/dt</code> of a state
36   * vector <code>Y</code>, both being one dimensional arrays. From the
37   * integrator point of view, this derivative depends only on the
38   * current time <code>t</code> and on the state vector
39   * <code>Y</code>.</p>
40   *
41   * <p>For real problems, the derivative depends also on parameters
42   * that do not belong to the state vector (dynamical model constants
43   * for example). These constants are completely outside of the scope
44   * of this interface, the classes that implement it are allowed to
45   * handle them as they want.</p>
46   *
47   * @see FieldODEIntegrator
48   *
49   * @param <T> the type of the field elements
50   */
51  
52  public interface FieldOrdinaryDifferentialEquation<T extends CalculusFieldElement<T>> {
53  
54      /** Get the dimension of the problem.
55       * @return dimension of the problem
56       */
57      int getDimension();
58  
59      /** Initialize equations at the start of an ODE integration.
60       * <p>
61       * This method is called once at the start of the integration. It
62       * may be used by the equations to initialize some internal data
63       * if needed.
64       * </p>
65       * <p>
66       * The default implementation does nothing.
67       * </p>
68       * @param t0 value of the independent <I>time</I> variable at integration start
69       * @param y0 array containing the value of the state vector at integration start
70       * @param finalTime target time for the integration
71       */
72      default void init(T t0, T[] y0, T finalTime) {
73          // do nothing by default
74      }
75  
76      /** Get the current time derivative of the state vector.
77       * @param t current value of the independent <I>time</I> variable
78       * @param y array containing the current value of the state vector
79       * @return time derivative of the state vector
80       */
81      T[] computeDerivatives(T t, T[] y);
82  
83  }