1   /* Copyright 2002-2025 CS GROUP
2    * Licensed to CS GROUP (CS) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * CS 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  package org.orekit.forces.maneuvers.jacobians;
18  
19  import org.orekit.propagation.AdditionalDataProvider;
20  import org.orekit.propagation.SpacecraftState;
21  
22  /** Generator for one column of a Jacobian matrix for special case of maneuver duration.
23   * <p>
24   * Typical use cases for this are estimation of maneuver duration during
25   * either orbit determination or maneuver optimization.
26   * </p>
27   * @author Luc Maisonobe
28   * @since 11.1
29   * @see MedianDate
30   * @see TriggerDate
31   */
32  public class Duration implements AdditionalDataProvider<double[]> {
33  
34      /** Name of the parameter corresponding to the start date. */
35      private final String startName;
36  
37      /** Name of the parameter corresponding to the stop date. */
38      private final String stopName;
39  
40      /** Name of the parameter corresponding to the column. */
41      private final String columnName;
42  
43      /** Simple constructor.
44       * @param startName name of the parameter corresponding to the start date
45       * @param stopName name of the parameter corresponding to the stop date
46       * @param columnName name of the parameter corresponding to the column
47       */
48      public Duration(final String startName, final String stopName, final String columnName) {
49          this.startName  = startName;
50          this.stopName   = stopName;
51          this.columnName = columnName;
52      }
53  
54      /** {@inheritDoc} */
55      @Override
56      public String getName() {
57          return columnName;
58      }
59  
60      /** {@inheritDoc}
61       * <p>
62       * The column state can be computed only if the start and stop dates columns are available.
63       * </p>
64       */
65      @Override
66      public boolean yields(final SpacecraftState state) {
67          return !(state.hasAdditionalData(startName) && state.hasAdditionalData(stopName));
68      }
69  
70      /** {@inheritDoc} */
71      @Override
72      public double[] getAdditionalData(final SpacecraftState state) {
73  
74          // compute partial derivatives with respect to start and stop dates
75          final double[] dYdT0 = state.getAdditionalState(startName);
76          final double[] dYdT1 = state.getAdditionalState(stopName);
77  
78          // combine derivatives to get partials with respect to duration
79          final double[] dYdTm = new double[dYdT0.length];
80          for (int i = 0; i < dYdTm.length; ++i) {
81              dYdTm[i] = 0.5 * (dYdT1[i] - dYdT0[i]);
82          }
83          return dYdTm;
84  
85      }
86  
87  }
88