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.math4.legacy.ode;
19
20 import org.apache.commons.math4.legacy.core.RealFieldElement;
21
22 /** This interface represents a first order differential equations set.
23 *
24 * <p>This interface should be implemented by all real first order
25 * differential equation problems before they can be handled by the
26 * integrators {@link FirstOrderIntegrator#integrate} method.</p>
27 *
28 * <p>A first order differential equations problem, as seen by an
29 * integrator is the time derivative <code>dY/dt</code> of a state
30 * vector <code>Y</code>, both being one dimensional arrays. From the
31 * integrator point of view, this derivative depends only on the
32 * current time <code>t</code> and on the state vector
33 * <code>Y</code>.</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 FirstOrderFieldIntegrator
42 *
43 * @param <T> the type of the field elements
44 * @since 3.6
45 */
46
47 public interface FirstOrderFieldDifferentialEquations<T extends RealFieldElement<T>> {
48
49 /** Get the dimension of the problem.
50 * @return dimension of the problem
51 */
52 int getDimension();
53
54 /** Initialize equations at the start of an ODE integration.
55 * <p>
56 * This method is called once at the start of the integration. It
57 * may be used by the equations to initialize some internal data
58 * if needed.
59 * </p>
60 * @param t0 value of the independent <I>time</I> variable at integration start
61 * @param y0 array containing the value of the state vector at integration start
62 * @param finalTime target time for the integration
63 */
64 void init(T t0, T[] y0, T finalTime);
65
66 /** Get the current time derivative of the state vector.
67 * @param t current value of the independent <I>time</I> variable
68 * @param y array containing the current value of the state vector
69 * @return time derivative of the state vector
70 */
71 T[] computeDerivatives(T t, T[] y);
72 }