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.semianalytical.dsst.utilities;
18  
19  import org.hipparchus.Field;
20  import org.hipparchus.CalculusFieldElement;
21  import org.hipparchus.util.MathArrays;
22  
23  /** Interpolation grid where a fixed number of points are
24   * evenly spaced between the start and the end of the integration step.
25   * <p>
26   * The grid is adapted to the step considered,
27   * meaning that for short steps, the grid will be dense,
28   * while for long steps the points will be far away one from each other
29   * </p>
30   */
31  public class FieldFixedNumberInterpolationGrid<T extends CalculusFieldElement<T>> implements FieldInterpolationGrid<T> {
32  
33      /** Number of points in the grid per step. */
34      private final int pointsPerStep;
35  
36      /** Field used by default. */
37      private final Field<T> field;
38  
39      /** Constructor.
40       * @param field field used by default
41       * @param pointsPerStep number of points in the grid per step
42       */
43      public FieldFixedNumberInterpolationGrid(final Field<T> field, final int pointsPerStep) {
44          this.field = field;
45          this.pointsPerStep = pointsPerStep;
46      }
47  
48      /** {@inheritDoc} */
49      @Override
50      public T[] getGridPoints(final T stepStart, final T stepEnd) {
51          final T[] grid = MathArrays.buildArray(field, pointsPerStep);
52  
53          final T stepSize = (stepEnd.subtract(stepStart)).divide(pointsPerStep - 1);
54          for (int i = 0; i < pointsPerStep; i++) {
55              grid[i] = stepSize.multiply(i).add(stepStart);
56          }
57  
58          return grid;
59      }
60  
61  }