1   /* Copyright 2002-2021 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.propagation.integration;
18  
19  import org.hipparchus.analysis.differentiation.Gradient;
20  import org.hipparchus.geometry.euclidean.threed.FieldRotation;
21  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
22  
23  /** Converter for states and parameters arrays.
24   *  @author Luc Maisonobe
25   *  @author Bryan Cazabonne
26   *  @since 10.2
27   */
28  public abstract class AbstractGradientConverter {
29  
30      /** Dimension of the state. */
31      private final int freeStateParameters;
32  
33      /** Simple constructor.
34       * @param freeStateParameters number of free parameters
35       */
36      protected AbstractGradientConverter(final int freeStateParameters) {
37          this.freeStateParameters = freeStateParameters;
38      }
39  
40      /** Get the number of free state parameters.
41       * @return number of free state parameters
42       */
43      public int getFreeStateParameters() {
44          return freeStateParameters;
45      }
46  
47      /** Add zero derivatives.
48       * @param original original scalar
49       * @param freeParameters total number of free parameters in the gradient
50       * @return extended scalar
51       */
52      protected Gradient extend(final Gradient original, final int freeParameters) {
53          final double[] originalDerivatives = original.getGradient();
54          final double[] extendedDerivatives = new double[freeParameters];
55          System.arraycopy(originalDerivatives, 0, extendedDerivatives, 0, originalDerivatives.length);
56          return new Gradient(original.getValue(), extendedDerivatives);
57      }
58  
59      /** Add zero derivatives.
60       * @param original original vector
61       * @param freeParameters total number of free parameters in the gradient
62       * @return extended vector
63       */
64      protected FieldVector3D<Gradient> extend(final FieldVector3D<Gradient> original, final int freeParameters) {
65          return new FieldVector3D<>(extend(original.getX(), freeParameters),
66                                     extend(original.getY(), freeParameters),
67                                     extend(original.getZ(), freeParameters));
68      }
69  
70      /** Add zero derivatives.
71       * @param original original rotation
72       * @param freeParameters total number of free parameters in the gradient
73       * @return extended rotation
74       */
75      protected FieldRotation<Gradient> extend(final FieldRotation<Gradient> original, final int freeParameters) {
76          return new FieldRotation<>(extend(original.getQ0(), freeParameters),
77                                     extend(original.getQ1(), freeParameters),
78                                     extend(original.getQ2(), freeParameters),
79                                     extend(original.getQ3(), freeParameters),
80                                     false);
81      }
82  }