1   /* Copyright 2002-2026 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 java.util.stream.IntStream;
20  import org.hipparchus.CalculusFieldElement;
21  import org.hipparchus.util.MathArrays;
22  
23  /**
24   * Base class for DSST interpolation grid methods.
25   * @author Luc Maisonobe
26   * @author Nicolas Bernard
27   * @author Bryan Cazabonne
28   * @since 14.0
29   */
30  abstract class AbstractInterpolationGrid implements InterpolationGrid {
31  
32      /** Constructor. */
33      protected AbstractInterpolationGrid() {
34          // nothing
35      }
36  
37      /** {@inheritDoc} */
38      @Override
39      public double[] getGridPoints(final double stepStart, final double stepEnd) {
40          final int pointsPerStep = getPointsPerStep(stepStart, stepEnd);
41          final double stepSize = (stepEnd - stepStart) / (pointsPerStep - 1);
42          return IntStream.range(0, pointsPerStep).mapToDouble(i -> stepSize * i + stepStart).toArray();
43      }
44  
45      /** {@inheritDoc} */
46      @Override
47      public <T extends CalculusFieldElement<T>> T[] getGridPoints(final T stepStart, final T stepEnd) {
48          final int pointsPerStep = getPointsPerStep(stepStart, stepEnd);
49          final T[] grid = MathArrays.buildArray(stepStart.getField(), pointsPerStep);
50          final T stepSize = stepEnd.subtract(stepStart).divide(pointsPerStep - 1.);
51          IntStream.range(0, pointsPerStep).forEach(i -> grid[i] = stepSize.multiply(i).add(stepStart));
52          return grid;
53      }
54  
55      /**
56       * Get the number of points in the grid per step.
57       * @param stepStart start of the step
58       * @param stepEnd end of the step
59       * @return the number of points in the grid per step
60       */
61      protected abstract int getPointsPerStep(double stepStart, double stepEnd);
62  
63      /**
64       * Get the number of points in the grid per step.
65       * @param stepStart start of the step
66       * @param stepEnd end of the step
67       * @param <T> type of field elements
68       * @return the number of points in the grid per step
69       */
70      protected <T extends CalculusFieldElement<T>> int getPointsPerStep(final T stepStart, final T stepEnd) {
71          return getPointsPerStep(stepStart.getReal(), stepEnd.getReal());
72      }
73  
74  }