001/*
002*   AbstractEvaluatable1D  -- A partial implementation of 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 * A class that defines a 1D function <code>y = fn(x)</code> (named "function") that can
025 * be called by math tools such as root finders. Also defines the derivative of the
026 * function. <code>dy/dx = dfn(x)/dx</code> (oddly enough, named "derivative"). An
027 * optional capability of setting an initial function value is also provided. This aides
028 * the calculating of some functions and is a common enough problem that I've included it
029 * in the basic {@link Evaluatable1D} class definition.
030 *
031 * <p> Modified by: Joseph A. Huwaldt  </p>
032 *
033 * @author Joseph A. Huwaldt Date: October 7, 1998
034 * @version February 23, 2025
035 */
036public abstract class AbstractEvaluatable1D implements Evaluatable1D {
037
038    private double value0;
039
040    /**
041     * Calculates the derivative of the function <code>dy/dx = d fn(x)/dx</code>. Classes
042     * wanting to return the derivative of the function at x should override this
043     * function. If the method using this class doesn't require the derivative, do nothing
044     * and Double.NaN is returned.
045     *
046     * @param x Independent parameter to the function.
047     * @return The function value at x or Double.NaN if the derivative is not defined.
048     * @throws RootException if there is any problem calculating the derivative.
049     */
050    @Override
051    public double derivative(double x) throws RootException {
052        return Double.NaN;
053    }
054
055    /**
056     * Used to set an initial function value (or any other initial value the user wants to
057     * use). This function is provided as an optional service. The programmer may use this
058     * to aide in solving problems where you want to find the point where
059     * <code>f(x) - f0 = 0</code>. Use this function to set f0 and use "getInitialValue()"
060     * to retrieve f0 and calculate f(x) - f0 in your "function()" definition.  </p>
061     *
062     * @param initialValue Initial function value, f0.
063     */
064    public void setInitialValue(double initialValue) {
065        value0 = initialValue;
066    }
067
068    /**
069     * Returns the initial function value set with "setInitialValue()".
070     *
071     * @return The initial value set with "setInitialValue()".
072     */
073    public final double getInitialValue() {
074        return value0;
075    }
076
077}