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
18package org.apache.commons.math.ode.sampling;
19
20import java.io.Externalizable;
21
22import org.apache.commons.math.ode.DerivativeException;
23
24/** This interface represents an interpolator over the last step
25 * during an ODE integration.
26 *
27 * <p>The various ODE integrators provide objects implementing this
28 * interface to the step handlers. These objects are often custom
29 * objects tightly bound to the integrator internal algorithms. The
30 * handlers can use these objects to retrieve the state vector at
31 * intermediate times between the previous and the current grid points
32 * (this feature is often called dense output).</p>
33 * <p>One important thing to note is that the step handlers may be so
34 * tightly bound to the integrators that they often share some internal
35 * state arrays. This imply that one should <em>never</em> use a direct
36 * reference to a step interpolator outside of the step handler, either
37 * for future use or for use in another thread. If such a need arise, the
38 * step interpolator <em>must</em> be copied using the dedicated
39 * {@link #copy()} method.
40 * </p>
41 *
42 * @see org.apache.commons.math.ode.FirstOrderIntegrator
43 * @see org.apache.commons.math.ode.SecondOrderIntegrator
44 * @see StepHandler
45 * @version $Revision: 1073158 $ $Date: 2011-02-21 22:46:52 +0100 (lun. 21 févr. 2011) $
46 * @since 1.2
47 */
48
49public interface StepInterpolator extends Externalizable {
50
51  /**
52   * Get the previous grid point time.
53   * @return previous grid point time
54   */
55  double getPreviousTime();
56
57  /**
58   * Get the current grid point time.
59   * @return current grid point time
60   */
61  double getCurrentTime();
62
63  /**
64   * Get the time of the interpolated point.
65   * If {@link #setInterpolatedTime} has not been called, it returns
66   * the current grid point time.
67   * @return interpolation point time
68   */
69  double getInterpolatedTime();
70
71  /**
72   * Set the time of the interpolated point.
73   * <p>Setting the time outside of the current step is now allowed, but
74   * should be used with care since the accuracy of the interpolator will
75   * probably be very poor far from this step. This allowance has been
76   * added to simplify implementation of search algorithms near the
77   * step endpoints.</p>
78   * <p>Setting the time changes the instance internal state. If a
79   * specific state must be preserved, a copy of the instance must be
80   * created using {@link #copy()}.</p>
81   * @param time time of the interpolated point
82   */
83  void setInterpolatedTime(double time);
84
85  /**
86   * Get the state vector of the interpolated point.
87   * <p>The returned vector is a reference to a reused array, so
88   * it should not be modified and it should be copied if it needs
89   * to be preserved across several calls.</p>
90   * @return state vector at time {@link #getInterpolatedTime}
91   * @see #getInterpolatedDerivatives()
92   * @exception DerivativeException if user code called from step interpolator
93   * finalization triggers one
94   */
95  double[] getInterpolatedState() throws DerivativeException;
96
97  /**
98   * Get the derivatives of the state vector of the interpolated point.
99   * <p>The returned vector is a reference to a reused array, so
100   * it should not be modified and it should be copied if it needs
101   * to be preserved across several calls.</p>
102   * @return derivatives of the state vector at time {@link #getInterpolatedTime}
103   * @see #getInterpolatedState()
104   * @exception DerivativeException if user code called from step interpolator
105   * finalization triggers one
106   * @since 2.0
107   */
108  double[] getInterpolatedDerivatives() throws DerivativeException;
109
110  /** Check if the natural integration direction is forward.
111   * <p>This method provides the integration direction as specified by
112   * the integrator itself, it avoid some nasty problems in
113   * degenerated cases like null steps due to cancellation at step
114   * initialization, step control or discrete events
115   * triggering.</p>
116   * @return true if the integration variable (time) increases during
117   * integration
118   */
119  boolean isForward();
120
121  /** Copy the instance.
122   * <p>The copied instance is guaranteed to be independent from the
123   * original one. Both can be used with different settings for
124   * interpolated time without any side effect.</p>
125   * @return a deep copy of the instance, which can be used independently.
126   * @exception DerivativeException if user code called from step interpolator
127   * finalization triggers one
128   * @see #setInterpolatedTime(double)
129   */
130   StepInterpolator copy() throws DerivativeException;
131
132}
133