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 }