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.sampling;
19
20 import org.apache.commons.math4.legacy.core.RealFieldElement;
21 import org.apache.commons.math4.legacy.ode.FieldODEStateAndDerivative;
22
23 /** This interface represents an interpolator over the last step
24 * during an ODE integration.
25 *
26 * <p>The various ODE integrators provide objects implementing this
27 * interface to the step handlers. These objects are often custom
28 * objects tightly bound to the integrator internal algorithms. The
29 * handlers can use these objects to retrieve the state vector at
30 * intermediate times between the previous and the current grid points
31 * (this feature is often called dense output).</p>
32 *
33 * @param <T> the type of the field elements
34 * @see org.apache.commons.math4.legacy.ode.FirstOrderFieldIntegrator
35 * @see FieldStepHandler
36 * @since 3.6
37 */
38
39 public interface FieldStepInterpolator<T extends RealFieldElement<T>> {
40
41 /**
42 * Get the state at previous grid point time.
43 * @return state at previous grid point time
44 */
45 FieldODEStateAndDerivative<T> getPreviousState();
46
47 /**
48 * Get the state at current grid point time.
49 * @return state at current grid point time
50 */
51 FieldODEStateAndDerivative<T> getCurrentState();
52
53 /**
54 * Get the state at interpolated time.
55 * <p>Setting the time outside of the current step is allowed, but
56 * should be used with care since the accuracy of the interpolator will
57 * probably be very poor far from this step. This allowance has been
58 * added to simplify implementation of search algorithms near the
59 * step endpoints.</p>
60 * @param time time of the interpolated point
61 * @return state at interpolated time
62 */
63 FieldODEStateAndDerivative<T> getInterpolatedState(T time);
64
65 /** Check if the natural integration direction is forward.
66 * <p>This method provides the integration direction as specified by
67 * the integrator itself, it avoid some nasty problems in
68 * degenerated cases like null steps due to cancellation at step
69 * initialization, step control or discrete events
70 * triggering.</p>
71 * @return true if the integration variable (time) increases during
72 * integration
73 */
74 boolean isForward();
75 }