| /* |
| * Copyright 2003-2004 The Apache Software Foundation. |
| * |
| * Licensed 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, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.commons.math.analysis; |
| |
| import java.io.Serializable; |
| |
| /** |
| * Immutable representation of a real polynomial function with real coefficients. |
| * <p> |
| * <a href="http://mathworld.wolfram.com/HornersMethod.html">Horner's Method</a> |
| * is used to evaluate the function. |
| * |
| * @version $Revision$ $Date$ |
| */ |
| public class PolynomialFunction implements DifferentiableUnivariateRealFunction, Serializable { |
| |
| /** Serializable version identifier */ |
| static final long serialVersionUID = 3322454535052136809L; |
| |
| /** |
| * The coefficients of the polynomial, ordered by degree -- i.e., |
| * coefficients[0] is the constant term and coefficients[n] is the |
| * coefficient of x^n where n is the degree of the polynomial. |
| */ |
| private double coefficients[]; |
| |
| /** |
| * Construct a polynomial with the given coefficients. The first element |
| * of the coefficients array is the constant term. Higher degree |
| * coefficients follow in sequence. The degree of the resulting polynomial |
| * is the length of the array minus 1. |
| * <p> |
| * The constructor makes a copy of the input array and assigns the copy to |
| * the coefficients property. |
| * |
| * @param c polynominal coefficients |
| * @throws NullPointerException if c is null |
| * @throws IllegalArgumentException if c is empty |
| */ |
| public PolynomialFunction(double c[]) { |
| super(); |
| if (c.length < 1) { |
| throw new IllegalArgumentException("Polynomial coefficient array must have postive length."); |
| } |
| this.coefficients = new double[c.length]; |
| System.arraycopy(c, 0, this.coefficients, 0, c.length); |
| } |
| |
| /** |
| * Compute the value of the function for the given argument. |
| * <p> |
| * The value returned is <br> |
| * <code>coefficients[n] * x^n + ... + coefficients[1] * x + coefficients[0]</code> |
| * |
| * @param x the argument for which the function value should be computed |
| * @return the value of the polynomial at the given point |
| * @see UnivariateRealFunction#value(double) |
| */ |
| public double value(double x) { |
| return evaluate(coefficients, x); |
| } |
| |
| |
| /** |
| * Returns the degree of the polynomial |
| * |
| * @return the degree of the polynomial |
| */ |
| public int degree() { |
| return coefficients.length - 1; |
| } |
| |
| /** |
| * Returns a copy of the coefficients array. |
| * <p> |
| * Changes made to the returned copy will not affect the coefficients of |
| * the polynomial. |
| * |
| * @return a fresh copy of the coefficients array |
| */ |
| public double[] getCoefficients() { |
| double[] out = new double[coefficients.length]; |
| System.arraycopy(coefficients,0, out, 0, coefficients.length); |
| return out; |
| } |
| |
| /** |
| * Uses Horner's Method to evaluate the polynomial with the given coefficients at |
| * the argument. |
| * |
| * @param coefficients the coefficients of the polynomial to evaluate |
| * @param argument the input value |
| * @return the value of the polynomial |
| * @throws IllegalArgumentException if coefficients is empty |
| * @throws NullPointerException if coefficients is null |
| */ |
| protected static double evaluate(double[] coefficients, double argument) { |
| int n = coefficients.length; |
| if (n < 1) { |
| throw new IllegalArgumentException("Coefficient array must have positive length for evaluation"); |
| } |
| double result = coefficients[n - 1]; |
| for (int j = n -2; j >=0; j--) { |
| result = argument * result + coefficients[j]; |
| } |
| return result; |
| } |
| |
| /** |
| * Returns the coefficients of the derivative of the polynomial with the given coefficients. |
| * |
| * @param coefficients the coefficients of the polynomial to differentiate |
| * @return the coefficients of the derivative or null if coefficients has length 1. |
| * @throws IllegalArgumentException if coefficients is empty |
| * @throws NullPointerException if coefficients is null |
| */ |
| protected static double[] differentiate(double[] coefficients) { |
| int n = coefficients.length; |
| if (n < 1) { |
| throw new IllegalArgumentException("Coefficient array must have positive length for differentiation"); |
| } |
| if (n == 1) { |
| return new double[]{0}; |
| } |
| double[] result = new double[n - 1]; |
| for (int i = n - 1; i > 0; i--) { |
| result[i - 1] = (double) i * coefficients[i]; |
| } |
| return result; |
| } |
| |
| /** |
| * Returns the derivative as a PolynomialRealFunction |
| * |
| * @return the derivative polynomial |
| */ |
| public PolynomialFunction polynomialDerivative() { |
| return new PolynomialFunction(differentiate(coefficients)); |
| } |
| |
| /** |
| * Returns the derivative as a UnivariateRealFunction |
| * |
| * @return the derivative function |
| */ |
| public UnivariateRealFunction derivative() { |
| return polynomialDerivative(); |
| } |
| |
| } |