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+/*
+ * 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.math3.analysis.polynomials;
+
+import org.apache.commons.math3.analysis.differentiation.DerivativeStructure;
+import org.apache.commons.math3.analysis.differentiation.UnivariateDifferentiableFunction;
+import org.apache.commons.math3.exception.DimensionMismatchException;
+import org.apache.commons.math3.exception.NoDataException;
+import org.apache.commons.math3.exception.NullArgumentException;
+import org.apache.commons.math3.exception.util.LocalizedFormats;
+import org.apache.commons.math3.util.MathUtils;
+
+/**
+ * Implements the representation of a real polynomial function in
+ * Newton Form. For reference, see <b>Elementary Numerical Analysis</b>,
+ * ISBN 0070124477, chapter 2.
+ * <p>
+ * The formula of polynomial in Newton form is
+ * p(x) = a[0] + a[1](x-c[0]) + a[2](x-c[0])(x-c[1]) + ... +
+ * a[n](x-c[0])(x-c[1])...(x-c[n-1])
+ * Note that the length of a[] is one more than the length of c[]</p>
+ *
+ * @since 1.2
+ */
+public class PolynomialFunctionNewtonForm implements UnivariateDifferentiableFunction {
+
+ /**
+ * 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[];
+
+ /**
+ * Centers of the Newton polynomial.
+ */
+ private final double c[];
+
+ /**
+ * When all c[i] = 0, a[] becomes normal polynomial coefficients,
+ * i.e. a[i] = coefficients[i].
+ */
+ private final double a[];
+
+ /**
+ * Whether the polynomial coefficients are available.
+ */
+ private boolean coefficientsComputed;
+
+ /**
+ * Construct a Newton polynomial with the given a[] and c[]. The order of
+ * centers are important in that if c[] shuffle, then values of a[] would
+ * completely change, not just a permutation of old a[].
+ * <p>
+ * The constructor makes copy of the input arrays and assigns them.</p>
+ *
+ * @param a Coefficients in Newton form formula.
+ * @param c Centers.
+ * @throws NullArgumentException if any argument is {@code null}.
+ * @throws NoDataException if any array has zero length.
+ * @throws DimensionMismatchException if the size difference between
+ * {@code a} and {@code c} is not equal to 1.
+ */
+ public PolynomialFunctionNewtonForm(double a[], double c[])
+ throws NullArgumentException, NoDataException, DimensionMismatchException {
+
+ verifyInputArray(a, c);
+ this.a = new double[a.length];
+ this.c = new double[c.length];
+ System.arraycopy(a, 0, this.a, 0, a.length);
+ System.arraycopy(c, 0, this.c, 0, c.length);
+ coefficientsComputed = false;
+ }
+
+ /**
+ * Calculate the function value at the given point.
+ *
+ * @param z Point at which the function value is to be computed.
+ * @return the function value.
+ */
+ public double value(double z) {
+ return evaluate(a, c, z);
+ }
+
+ /**
+ * {@inheritDoc}
+ * @since 3.1
+ */
+ public DerivativeStructure value(final DerivativeStructure t) {
+ verifyInputArray(a, c);
+
+ final int n = c.length;
+ DerivativeStructure value = new DerivativeStructure(t.getFreeParameters(), t.getOrder(), a[n]);
+ for (int i = n - 1; i >= 0; i--) {
+ value = t.subtract(c[i]).multiply(value).add(a[i]);
+ }
+
+ return value;
+
+ }
+
+ /**
+ * Returns the degree of the polynomial.
+ *
+ * @return the degree of the polynomial
+ */
+ public int degree() {
+ return c.length;
+ }
+
+ /**
+ * Returns a copy of coefficients in Newton form formula.
+ * <p>
+ * Changes made to the returned copy will not affect the polynomial.</p>
+ *
+ * @return a fresh copy of coefficients in Newton form formula
+ */
+ public double[] getNewtonCoefficients() {
+ double[] out = new double[a.length];
+ System.arraycopy(a, 0, out, 0, a.length);
+ return out;
+ }
+
+ /**
+ * Returns a copy of the centers array.
+ * <p>
+ * Changes made to the returned copy will not affect the polynomial.</p>
+ *
+ * @return a fresh copy of the centers array.
+ */
+ public double[] getCenters() {
+ double[] out = new double[c.length];
+ System.arraycopy(c, 0, out, 0, c.length);
+ return out;
+ }
+
+ /**
+ * Returns a copy of the coefficients array.
+ * <p>
+ * Changes made to the returned copy will not affect the polynomial.</p>
+ *
+ * @return a fresh copy of the coefficients array.
+ */
+ public double[] getCoefficients() {
+ if (!coefficientsComputed) {
+ computeCoefficients();
+ }
+ double[] out = new double[coefficients.length];
+ System.arraycopy(coefficients, 0, out, 0, coefficients.length);
+ return out;
+ }
+
+ /**
+ * Evaluate the Newton polynomial using nested multiplication. It is
+ * also called <a href="http://mathworld.wolfram.com/HornersRule.html">
+ * Horner's Rule</a> and takes O(N) time.
+ *
+ * @param a Coefficients in Newton form formula.
+ * @param c Centers.
+ * @param z Point at which the function value is to be computed.
+ * @return the function value.
+ * @throws NullArgumentException if any argument is {@code null}.
+ * @throws NoDataException if any array has zero length.
+ * @throws DimensionMismatchException if the size difference between
+ * {@code a} and {@code c} is not equal to 1.
+ */
+ public static double evaluate(double a[], double c[], double z)
+ throws NullArgumentException, DimensionMismatchException, NoDataException {
+ verifyInputArray(a, c);
+
+ final int n = c.length;
+ double value = a[n];
+ for (int i = n - 1; i >= 0; i--) {
+ value = a[i] + (z - c[i]) * value;
+ }
+
+ return value;
+ }
+
+ /**
+ * Calculate the normal polynomial coefficients given the Newton form.
+ * It also uses nested multiplication but takes O(N^2) time.
+ */
+ protected void computeCoefficients() {
+ final int n = degree();
+
+ coefficients = new double[n+1];
+ for (int i = 0; i <= n; i++) {
+ coefficients[i] = 0.0;
+ }
+
+ coefficients[0] = a[n];
+ for (int i = n-1; i >= 0; i--) {
+ for (int j = n-i; j > 0; j--) {
+ coefficients[j] = coefficients[j-1] - c[i] * coefficients[j];
+ }
+ coefficients[0] = a[i] - c[i] * coefficients[0];
+ }
+
+ coefficientsComputed = true;
+ }
+
+ /**
+ * Verifies that the input arrays are valid.
+ * <p>
+ * The centers must be distinct for interpolation purposes, but not
+ * for general use. Thus it is not verified here.</p>
+ *
+ * @param a the coefficients in Newton form formula
+ * @param c the centers
+ * @throws NullArgumentException if any argument is {@code null}.
+ * @throws NoDataException if any array has zero length.
+ * @throws DimensionMismatchException if the size difference between
+ * {@code a} and {@code c} is not equal to 1.
+ * @see org.apache.commons.math3.analysis.interpolation.DividedDifferenceInterpolator#computeDividedDifference(double[],
+ * double[])
+ */
+ protected static void verifyInputArray(double a[], double c[])
+ throws NullArgumentException, NoDataException, DimensionMismatchException {
+ MathUtils.checkNotNull(a);
+ MathUtils.checkNotNull(c);
+ if (a.length == 0 || c.length == 0) {
+ throw new NoDataException(LocalizedFormats.EMPTY_POLYNOMIALS_COEFFICIENTS_ARRAY);
+ }
+ if (a.length != c.length + 1) {
+ throw new DimensionMismatchException(LocalizedFormats.ARRAY_SIZES_SHOULD_HAVE_DIFFERENCE_1,
+ a.length, c.length);
+ }
+ }
+
+}