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 /** This interface represents a first order differential equations set.
21 *
22 * <p>This interface should be implemented by all real first order
23 * differential equation problems before they can be handled by the
24 * integrators {@link ODEIntegrator#integrate(OrdinaryDifferentialEquation,
25 * ODEState, double)} 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 ODEIntegrator
41 * @see FirstOrderConverter
42 * @see SecondOrderODE
43 *
44 */
45 public interface OrdinaryDifferentialEquation {
46
47 /** Get the dimension of the problem.
48 * @return dimension of the problem
49 */
50 int getDimension();
51
52 /** Initialize equations at the start of an ODE integration.
53 * <p>
54 * This method is called once at the start of the integration. It
55 * may be used by the equations to initialize some internal data
56 * if needed.
57 * </p>
58 * <p>
59 * The default implementation does nothing.
60 * </p>
61 * @param t0 value of the independent <I>time</I> variable at integration start
62 * @param y0 array containing the value of the state vector at integration start
63 * @param finalTime target time for the integration
64 */
65 default void init(double t0, double[] y0, double finalTime) {
66 // do nothing by default
67 }
68
69 /** Get the current time derivative of the state vector.
70 * @param t current value of the independent <I>time</I> variable
71 * @param y array containing the current value of the state vector
72 * @return time derivative of the state vector
73 */
74 double[] computeDerivatives(double t, double[] y);
75
76 }