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/*
 * Copyright (c) 2010-2021 Haifeng Li. All rights reserved.
 *
 * Smile is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Smile is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Smile.  If not, see .
 */

package smile.math;

/**
 * A differentiable function is a function whose derivative exists at each point
 * in its domain.
 *
 * @author Haifeng Li
 */
public interface DifferentiableFunction extends Function {
    /**
     * Computes the gradient/derivative at x.
     *
     * @param x a real number.
     * @return the derivative.
     */
    double g(double x);

    /**
     * Compute the second-order derivative at x.
     *
     * @param x a real number.
     * @return the second-order derivative.
     */
    default double g2(double x) {
        throw new UnsupportedOperationException();
    }
}