| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You 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.polynomials; |
| |
| import java.io.Serializable; |
| import java.util.Arrays; |
| |
| import org.apache.commons.math.exception.util.LocalizedFormats; |
| import org.apache.commons.math.exception.NoDataException; |
| import org.apache.commons.math.analysis.DifferentiableUnivariateRealFunction; |
| import org.apache.commons.math.analysis.UnivariateRealFunction; |
| import org.apache.commons.math.util.FastMath; |
| |
| /** |
| * 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.</p> |
| * |
| * @version $Revision: 1042376 $ $Date: 2010-12-05 16:54:55 +0100 (dim. 05 déc. 2010) $ |
| */ |
| public class PolynomialFunction implements DifferentiableUnivariateRealFunction, Serializable { |
| |
| /** |
| * Serialization identifier |
| */ |
| private static final long serialVersionUID = -7726511984200295583L; |
| |
| /** |
| * 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 final 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 index of the last non-null element of the array, or 0 if all elements |
| * are null. |
| * <p> |
| * The constructor makes a copy of the input array and assigns the copy to |
| * the coefficients property.</p> |
| * |
| * @param c polynomial coefficients |
| * @throws NullPointerException if c is null |
| * @throws NoDataException if c is empty |
| */ |
| public PolynomialFunction(double c[]) { |
| super(); |
| int n = c.length; |
| if (n == 0) { |
| throw new NoDataException(LocalizedFormats.EMPTY_POLYNOMIALS_COEFFICIENTS_ARRAY); |
| } |
| while ((n > 1) && (c[n - 1] == 0)) { |
| --n; |
| } |
| this.coefficients = new double[n]; |
| System.arraycopy(c, 0, this.coefficients, 0, n); |
| } |
| |
| /** |
| * 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> |
| * </p> |
| * |
| * @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.</p> |
| * |
| * @return a fresh copy of the coefficients array |
| */ |
| public double[] getCoefficients() { |
| return coefficients.clone(); |
| } |
| |
| /** |
| * 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 NoDataException if coefficients is empty |
| * @throws NullPointerException if coefficients is null |
| */ |
| protected static double evaluate(double[] coefficients, double argument) { |
| int n = coefficients.length; |
| if (n == 0) { |
| throw new NoDataException(LocalizedFormats.EMPTY_POLYNOMIALS_COEFFICIENTS_ARRAY); |
| } |
| double result = coefficients[n - 1]; |
| for (int j = n -2; j >=0; j--) { |
| result = argument * result + coefficients[j]; |
| } |
| return result; |
| } |
| |
| /** |
| * Add a polynomial to the instance. |
| * @param p polynomial to add |
| * @return a new polynomial which is the sum of the instance and p |
| */ |
| public PolynomialFunction add(final PolynomialFunction p) { |
| |
| // identify the lowest degree polynomial |
| final int lowLength = FastMath.min(coefficients.length, p.coefficients.length); |
| final int highLength = FastMath.max(coefficients.length, p.coefficients.length); |
| |
| // build the coefficients array |
| double[] newCoefficients = new double[highLength]; |
| for (int i = 0; i < lowLength; ++i) { |
| newCoefficients[i] = coefficients[i] + p.coefficients[i]; |
| } |
| System.arraycopy((coefficients.length < p.coefficients.length) ? |
| p.coefficients : coefficients, |
| lowLength, |
| newCoefficients, lowLength, |
| highLength - lowLength); |
| |
| return new PolynomialFunction(newCoefficients); |
| |
| } |
| |
| /** |
| * Subtract a polynomial from the instance. |
| * @param p polynomial to subtract |
| * @return a new polynomial which is the difference the instance minus p |
| */ |
| public PolynomialFunction subtract(final PolynomialFunction p) { |
| |
| // identify the lowest degree polynomial |
| int lowLength = FastMath.min(coefficients.length, p.coefficients.length); |
| int highLength = FastMath.max(coefficients.length, p.coefficients.length); |
| |
| // build the coefficients array |
| double[] newCoefficients = new double[highLength]; |
| for (int i = 0; i < lowLength; ++i) { |
| newCoefficients[i] = coefficients[i] - p.coefficients[i]; |
| } |
| if (coefficients.length < p.coefficients.length) { |
| for (int i = lowLength; i < highLength; ++i) { |
| newCoefficients[i] = -p.coefficients[i]; |
| } |
| } else { |
| System.arraycopy(coefficients, lowLength, newCoefficients, lowLength, |
| highLength - lowLength); |
| } |
| |
| return new PolynomialFunction(newCoefficients); |
| |
| } |
| |
| /** |
| * Negate the instance. |
| * @return a new polynomial |
| */ |
| public PolynomialFunction negate() { |
| double[] newCoefficients = new double[coefficients.length]; |
| for (int i = 0; i < coefficients.length; ++i) { |
| newCoefficients[i] = -coefficients[i]; |
| } |
| return new PolynomialFunction(newCoefficients); |
| } |
| |
| /** |
| * Multiply the instance by a polynomial. |
| * @param p polynomial to multiply by |
| * @return a new polynomial |
| */ |
| public PolynomialFunction multiply(final PolynomialFunction p) { |
| |
| double[] newCoefficients = new double[coefficients.length + p.coefficients.length - 1]; |
| |
| for (int i = 0; i < newCoefficients.length; ++i) { |
| newCoefficients[i] = 0.0; |
| for (int j = FastMath.max(0, i + 1 - p.coefficients.length); |
| j < FastMath.min(coefficients.length, i + 1); |
| ++j) { |
| newCoefficients[i] += coefficients[j] * p.coefficients[i-j]; |
| } |
| } |
| |
| return new PolynomialFunction(newCoefficients); |
| |
| } |
| |
| /** |
| * 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 NoDataException if coefficients is empty |
| * @throws NullPointerException if coefficients is null |
| */ |
| protected static double[] differentiate(double[] coefficients) { |
| int n = coefficients.length; |
| if (n == 0) { |
| throw new NoDataException(LocalizedFormats.EMPTY_POLYNOMIALS_COEFFICIENTS_ARRAY); |
| } |
| if (n == 1) { |
| return new double[]{0}; |
| } |
| double[] result = new double[n - 1]; |
| for (int i = n - 1; i > 0; i--) { |
| result[i - 1] = 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(); |
| } |
| |
| /** Returns a string representation of the polynomial. |
| |
| * <p>The representation is user oriented. Terms are displayed lowest |
| * degrees first. The multiplications signs, coefficients equals to |
| * one and null terms are not displayed (except if the polynomial is 0, |
| * in which case the 0 constant term is displayed). Addition of terms |
| * with negative coefficients are replaced by subtraction of terms |
| * with positive coefficients except for the first displayed term |
| * (i.e. we display <code>-3</code> for a constant negative polynomial, |
| * but <code>1 - 3 x + x^2</code> if the negative coefficient is not |
| * the first one displayed).</p> |
| |
| * @return a string representation of the polynomial |
| |
| */ |
| @Override |
| public String toString() { |
| |
| StringBuilder s = new StringBuilder(); |
| if (coefficients[0] == 0.0) { |
| if (coefficients.length == 1) { |
| return "0"; |
| } |
| } else { |
| s.append(Double.toString(coefficients[0])); |
| } |
| |
| for (int i = 1; i < coefficients.length; ++i) { |
| |
| if (coefficients[i] != 0) { |
| |
| if (s.length() > 0) { |
| if (coefficients[i] < 0) { |
| s.append(" - "); |
| } else { |
| s.append(" + "); |
| } |
| } else { |
| if (coefficients[i] < 0) { |
| s.append("-"); |
| } |
| } |
| |
| double absAi = FastMath.abs(coefficients[i]); |
| if ((absAi - 1) != 0) { |
| s.append(Double.toString(absAi)); |
| s.append(' '); |
| } |
| |
| s.append("x"); |
| if (i > 1) { |
| s.append('^'); |
| s.append(Integer.toString(i)); |
| } |
| } |
| |
| } |
| |
| return s.toString(); |
| |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public int hashCode() { |
| final int prime = 31; |
| int result = 1; |
| result = prime * result + Arrays.hashCode(coefficients); |
| return result; |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public boolean equals(Object obj) { |
| if (this == obj) |
| return true; |
| if (!(obj instanceof PolynomialFunction)) |
| return false; |
| PolynomialFunction other = (PolynomialFunction) obj; |
| if (!Arrays.equals(coefficients, other.coefficients)) |
| return false; |
| return true; |
| } |
| |
| } |