FieldMaxGapInterpolationGrid.java

/* Copyright 2002-2023 CS GROUP
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 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * CS licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
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package org.orekit.propagation.semianalytical.dsst.utilities;

import org.hipparchus.Field;
import org.hipparchus.CalculusFieldElement;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.MathArrays;

/** Interpolation grid where points obey a maximum time gap.
 * <p>
 * The grid is adapted to the step considered,
 * meaning that for short steps, the grid will have numerous points.
 * </p>
 *
 * @author Luc Maisonobe
 * @since 7.1
 * @param <T> type of the field elements
 */
public class FieldMaxGapInterpolationGrid <T extends CalculusFieldElement<T>> implements FieldInterpolationGrid<T> {

    /** Maximum time gap. */
    private final T maxGap;

    /** Field used by default. */
    private final Field<T> field;

    /** Constructor.
     * @param field field used by default
     * @param maxGap maximum time gap between interpolation points
     */
    public FieldMaxGapInterpolationGrid(final Field<T> field, final T maxGap) {
        this.field  = field;
        this.maxGap = maxGap;
    }

    /** {@inheritDoc} */
    @Override
    public T[] getGridPoints(final T stepStart, final T stepEnd) {
        final int pointsPerStep = FastMath.max(2, (int) FastMath.ceil(FastMath.abs(stepEnd.getReal() - stepStart.getReal()) / maxGap.getReal()));;
        final T[] grid = MathArrays.buildArray(field, pointsPerStep);

        final T stepSize = stepEnd.subtract(stepStart).divide(pointsPerStep - 1.);
        for (int i = 0; i < pointsPerStep; i++) {
            grid[i] = stepSize.multiply(i).add(stepStart);
        }

        return grid;
    }
}