001/*
002*   Evaluatable1D  -- Interface for a 1D function y=fn(x) and it's slope dy/dx=d_fn(x)/dx.
003*
004*   Copyright (C) 1999-2025, by Joseph A. Huwaldt. All rights reserved.
005*   
006*   This library is free software; you can redistribute it and/or
007*   modify it under the terms of the GNU Lesser General Public
008*   License as published by the Free Software Foundation; either
009*   version 2 of the License, or (at your option) any later version.
010*   
011*   This library is distributed in the hope that it will be useful,
012*   but WITHOUT ANY WARRANTY; without even the implied warranty of
013*   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014*   Lesser General Public License for more details.
015*
016*   You should have received a copy of the GNU Lesser General Public License
017*   along with this program; if not, write to the Free Software
018*   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
019*   Or visit:  http://www.gnu.org/licenses/lgpl.html
020*/
021package jahuwaldt.tools.math;
022
023/**
024 * An interface that defines a 1D function y = fn(x) (named "function") that can be called
025 * by math tools such as root finders. Also defines the derivative of the function. dy/dx
026 * = d fn(x)/dx (oddly enough, named "derivative").
027 *
028 * <p> Modified by: Joseph A. Huwaldt  </p>
029 *
030 * @author Joseph A. Huwaldt Date: October 7, 1998
031 * @version February 23, 2025
032 */
033public interface Evaluatable1D {
034
035    /**
036     * User supplied method that calculates the function y = fn(x). Classes implementing
037     * this interface must define this function.
038     *
039     * @param x Independent parameter to the function.
040     * @return The function value at x.
041     * @throws RootException if there is a problem computing the function.
042     */
043    public double function(double x) throws RootException;
044
045    /**
046     * Calculates the derivative of the function <code>dy/dx = d fn(x)/dx</code>. Classes
047     * wanting to return the derivative of the function at x should override this
048     * function. If the method using this class doesn't require the derivative, do nothing
049     * and Double.NaN is returned.
050     *
051     * @param x Independent parameter to the function.
052     * @return The function value at x or Double.NaN if the derivative is not defined.
053     * @throws RootException if there is a problem computing the derivative.
054     */
055    public double derivative(double x) throws RootException;
056
057}