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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.interpolation;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import org.apache.commons.math3.analysis.differentiation.DerivativeStructure;
+import org.apache.commons.math3.analysis.differentiation.UnivariateDifferentiableVectorFunction;
+import org.apache.commons.math3.analysis.polynomials.PolynomialFunction;
+import org.apache.commons.math3.exception.MathArithmeticException;
+import org.apache.commons.math3.exception.NoDataException;
+import org.apache.commons.math3.exception.ZeroException;
+import org.apache.commons.math3.exception.util.LocalizedFormats;
+import org.apache.commons.math3.util.CombinatoricsUtils;
+
+/** Polynomial interpolator using both sample values and sample derivatives.
+ * <p>
+ * The interpolation polynomials match all sample points, including both values
+ * and provided derivatives. There is one polynomial for each component of
+ * the values vector. All polynomials have the same degree. The degree of the
+ * polynomials depends on the number of points and number of derivatives at each
+ * point. For example the interpolation polynomials for n sample points without
+ * any derivatives all have degree n-1. The interpolation polynomials for n
+ * sample points with the two extreme points having value and first derivative
+ * and the remaining points having value only all have degree n+1. The
+ * interpolation polynomial for n sample points with value, first and second
+ * derivative for all points all have degree 3n-1.
+ * </p>
+ *
+ * @since 3.1
+ */
+public class HermiteInterpolator implements UnivariateDifferentiableVectorFunction {
+
+ /** Sample abscissae. */
+ private final List<Double> abscissae;
+
+ /** Top diagonal of the divided differences array. */
+ private final List<double[]> topDiagonal;
+
+ /** Bottom diagonal of the divided differences array. */
+ private final List<double[]> bottomDiagonal;
+
+ /** Create an empty interpolator.
+ */
+ public HermiteInterpolator() {
+ this.abscissae = new ArrayList<Double>();
+ this.topDiagonal = new ArrayList<double[]>();
+ this.bottomDiagonal = new ArrayList<double[]>();
+ }
+
+ /** Add a sample point.
+ * <p>
+ * This method must be called once for each sample point. It is allowed to
+ * mix some calls with values only with calls with values and first
+ * derivatives.
+ * </p>
+ * <p>
+ * The point abscissae for all calls <em>must</em> be different.
+ * </p>
+ * @param x abscissa of the sample point
+ * @param value value and derivatives of the sample point
+ * (if only one row is passed, it is the value, if two rows are
+ * passed the first one is the value and the second the derivative
+ * and so on)
+ * @exception ZeroException if the abscissa difference between added point
+ * and a previous point is zero (i.e. the two points are at same abscissa)
+ * @exception MathArithmeticException if the number of derivatives is larger
+ * than 20, which prevents computation of a factorial
+ */
+ public void addSamplePoint(final double x, final double[] ... value)
+ throws ZeroException, MathArithmeticException {
+
+ for (int i = 0; i < value.length; ++i) {
+
+ final double[] y = value[i].clone();
+ if (i > 1) {
+ double inv = 1.0 / CombinatoricsUtils.factorial(i);
+ for (int j = 0; j < y.length; ++j) {
+ y[j] *= inv;
+ }
+ }
+
+ // update the bottom diagonal of the divided differences array
+ final int n = abscissae.size();
+ bottomDiagonal.add(n - i, y);
+ double[] bottom0 = y;
+ for (int j = i; j < n; ++j) {
+ final double[] bottom1 = bottomDiagonal.get(n - (j + 1));
+ final double inv = 1.0 / (x - abscissae.get(n - (j + 1)));
+ if (Double.isInfinite(inv)) {
+ throw new ZeroException(LocalizedFormats.DUPLICATED_ABSCISSA_DIVISION_BY_ZERO, x);
+ }
+ for (int k = 0; k < y.length; ++k) {
+ bottom1[k] = inv * (bottom0[k] - bottom1[k]);
+ }
+ bottom0 = bottom1;
+ }
+
+ // update the top diagonal of the divided differences array
+ topDiagonal.add(bottom0.clone());
+
+ // update the abscissae array
+ abscissae.add(x);
+
+ }
+
+ }
+
+ /** Compute the interpolation polynomials.
+ * @return interpolation polynomials array
+ * @exception NoDataException if sample is empty
+ */
+ public PolynomialFunction[] getPolynomials()
+ throws NoDataException {
+
+ // safety check
+ checkInterpolation();
+
+ // iteration initialization
+ final PolynomialFunction zero = polynomial(0);
+ PolynomialFunction[] polynomials = new PolynomialFunction[topDiagonal.get(0).length];
+ for (int i = 0; i < polynomials.length; ++i) {
+ polynomials[i] = zero;
+ }
+ PolynomialFunction coeff = polynomial(1);
+
+ // build the polynomials by iterating on the top diagonal of the divided differences array
+ for (int i = 0; i < topDiagonal.size(); ++i) {
+ double[] tdi = topDiagonal.get(i);
+ for (int k = 0; k < polynomials.length; ++k) {
+ polynomials[k] = polynomials[k].add(coeff.multiply(polynomial(tdi[k])));
+ }
+ coeff = coeff.multiply(polynomial(-abscissae.get(i), 1.0));
+ }
+
+ return polynomials;
+
+ }
+
+ /** Interpolate value at a specified abscissa.
+ * <p>
+ * Calling this method is equivalent to call the {@link PolynomialFunction#value(double)
+ * value} methods of all polynomials returned by {@link #getPolynomials() getPolynomials},
+ * except it does not build the intermediate polynomials, so this method is faster and
+ * numerically more stable.
+ * </p>
+ * @param x interpolation abscissa
+ * @return interpolated value
+ * @exception NoDataException if sample is empty
+ */
+ public double[] value(double x)
+ throws NoDataException {
+
+ // safety check
+ checkInterpolation();
+
+ final double[] value = new double[topDiagonal.get(0).length];
+ double valueCoeff = 1;
+ for (int i = 0; i < topDiagonal.size(); ++i) {
+ double[] dividedDifference = topDiagonal.get(i);
+ for (int k = 0; k < value.length; ++k) {
+ value[k] += dividedDifference[k] * valueCoeff;
+ }
+ final double deltaX = x - abscissae.get(i);
+ valueCoeff *= deltaX;
+ }
+
+ return value;
+
+ }
+
+ /** Interpolate value at a specified abscissa.
+ * <p>
+ * Calling this method is equivalent to call the {@link
+ * PolynomialFunction#value(DerivativeStructure) value} methods of all polynomials
+ * returned by {@link #getPolynomials() getPolynomials}, except it does not build the
+ * intermediate polynomials, so this method is faster and numerically more stable.
+ * </p>
+ * @param x interpolation abscissa
+ * @return interpolated value
+ * @exception NoDataException if sample is empty
+ */
+ public DerivativeStructure[] value(final DerivativeStructure x)
+ throws NoDataException {
+
+ // safety check
+ checkInterpolation();
+
+ final DerivativeStructure[] value = new DerivativeStructure[topDiagonal.get(0).length];
+ Arrays.fill(value, x.getField().getZero());
+ DerivativeStructure valueCoeff = x.getField().getOne();
+ for (int i = 0; i < topDiagonal.size(); ++i) {
+ double[] dividedDifference = topDiagonal.get(i);
+ for (int k = 0; k < value.length; ++k) {
+ value[k] = value[k].add(valueCoeff.multiply(dividedDifference[k]));
+ }
+ final DerivativeStructure deltaX = x.subtract(abscissae.get(i));
+ valueCoeff = valueCoeff.multiply(deltaX);
+ }
+
+ return value;
+
+ }
+
+ /** Check interpolation can be performed.
+ * @exception NoDataException if interpolation cannot be performed
+ * because sample is empty
+ */
+ private void checkInterpolation() throws NoDataException {
+ if (abscissae.isEmpty()) {
+ throw new NoDataException(LocalizedFormats.EMPTY_INTERPOLATION_SAMPLE);
+ }
+ }
+
+ /** Create a polynomial from its coefficients.
+ * @param c polynomials coefficients
+ * @return polynomial
+ */
+ private PolynomialFunction polynomial(double ... c) {
+ return new PolynomialFunction(c);
+ }
+
+}