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Open-source constraint solver.

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/*
 * This file is part of choco-solver, http://choco-solver.org/
 *
 * Copyright (c) 2024, IMT Atlantique. All rights reserved.
 *
 * Licensed under the BSD 4-clause license.
 *
 * See LICENSE file in the project root for full license information.
 */
package org.chocosolver.solver.search.restart;

/**
 * A geometrical cutoff strategy.
 * It is based on two parameters: g for geometricalFactor and s for scaleFactor.
 * At step n, the next cutoff is computed with the following function : s*g^n
 * 

 * Example with s=1 and g=1.3:
 * 1, 2, 2, 3, 3, 4, 5, 7, 9, 11, 14, 18, 24, 31, 40, ...
 *
 * @author Charles Prud'homme, Arnaud Malapert
 * @since 13/05/11
 */
public final class GeometricalCutoff extends AbstractCutoff {

    /**
     * Declared geometrical factor
     */
    private final double geometricalFactor;
    /**
     * Current geometrical factor, after n calls to {@link #getNextCutoff()}.
     */
    private double geometricalFactorPower;

    /**
     * A geometrical cutoff strategy.
     * At step n, the next cutoff is computed with the following function : s*g^n
     * @param s scale factor
     * @param g geometrical factor
     * @exception IllegalArgumentException if g is not strictly greater than 1

     */
    @SuppressWarnings("WeakerAccess")
    public GeometricalCutoff(long s, double g) throws IllegalArgumentException{
        super(s);
        if (g <= 1) {
            throw new IllegalArgumentException("The geometrical factor of the restart strategy must be strictly greater than 1.");
        }
        this.geometricalFactor = g;
        this.geometricalFactorPower = 1;
    }

    /**
     * @return at call n, the next cutoff is computed with the following function :
     * s*g^n
     */
    @Override
    public long getNextCutoff() {
        final long cutoff = (long) Math.ceil(scaleFactor * geometricalFactorPower) * grower.getAsInt();
        geometricalFactorPower *= geometricalFactor;
        return cutoff;
    }

    @Override
    public void reset() {
        this.geometricalFactorPower = 1;
    }

    @Override
    public String toString() {
        return "GEOMETRICAL(s=" + scaleFactor + ", g=" + geometricalFactor + ')';
    }
}