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Diffstat (limited to 'src/main/java/org/apache/commons/math3/analysis/interpolation/BicubicInterpolatingFunction.java')
| -rw-r--r-- | src/main/java/org/apache/commons/math3/analysis/interpolation/BicubicInterpolatingFunction.java | 325 |
1 files changed, 325 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/math3/analysis/interpolation/BicubicInterpolatingFunction.java b/src/main/java/org/apache/commons/math3/analysis/interpolation/BicubicInterpolatingFunction.java new file mode 100644 index 0000000..454d8f8 --- /dev/null +++ b/src/main/java/org/apache/commons/math3/analysis/interpolation/BicubicInterpolatingFunction.java @@ -0,0 +1,325 @@ +/* + * 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.Arrays; +import org.apache.commons.math3.analysis.BivariateFunction; +import org.apache.commons.math3.exception.DimensionMismatchException; +import org.apache.commons.math3.exception.NoDataException; +import org.apache.commons.math3.exception.OutOfRangeException; +import org.apache.commons.math3.exception.NonMonotonicSequenceException; +import org.apache.commons.math3.util.MathArrays; + +/** + * Function that implements the + * <a href="http://en.wikipedia.org/wiki/Bicubic_interpolation"> + * bicubic spline interpolation</a>. + * + * @since 3.4 + */ +public class BicubicInterpolatingFunction + implements BivariateFunction { + /** Number of coefficients. */ + private static final int NUM_COEFF = 16; + /** + * Matrix to compute the spline coefficients from the function values + * and function derivatives values + */ + private static final double[][] AINV = { + { 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 }, + { 0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0 }, + { -3,3,0,0,-2,-1,0,0,0,0,0,0,0,0,0,0 }, + { 2,-2,0,0,1,1,0,0,0,0,0,0,0,0,0,0 }, + { 0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0 }, + { 0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0 }, + { 0,0,0,0,0,0,0,0,-3,3,0,0,-2,-1,0,0 }, + { 0,0,0,0,0,0,0,0,2,-2,0,0,1,1,0,0 }, + { -3,0,3,0,0,0,0,0,-2,0,-1,0,0,0,0,0 }, + { 0,0,0,0,-3,0,3,0,0,0,0,0,-2,0,-1,0 }, + { 9,-9,-9,9,6,3,-6,-3,6,-6,3,-3,4,2,2,1 }, + { -6,6,6,-6,-3,-3,3,3,-4,4,-2,2,-2,-2,-1,-1 }, + { 2,0,-2,0,0,0,0,0,1,0,1,0,0,0,0,0 }, + { 0,0,0,0,2,0,-2,0,0,0,0,0,1,0,1,0 }, + { -6,6,6,-6,-4,-2,4,2,-3,3,-3,3,-2,-1,-2,-1 }, + { 4,-4,-4,4,2,2,-2,-2,2,-2,2,-2,1,1,1,1 } + }; + + /** Samples x-coordinates */ + private final double[] xval; + /** Samples y-coordinates */ + private final double[] yval; + /** Set of cubic splines patching the whole data grid */ + private final BicubicFunction[][] splines; + + /** + * @param x Sample values of the x-coordinate, in increasing order. + * @param y Sample values of the y-coordinate, in increasing order. + * @param f Values of the function on every grid point. + * @param dFdX Values of the partial derivative of function with respect + * to x on every grid point. + * @param dFdY Values of the partial derivative of function with respect + * to y on every grid point. + * @param d2FdXdY Values of the cross partial derivative of function on + * every grid point. + * @throws DimensionMismatchException if the various arrays do not contain + * the expected number of elements. + * @throws NonMonotonicSequenceException if {@code x} or {@code y} are + * not strictly increasing. + * @throws NoDataException if any of the arrays has zero length. + */ + public BicubicInterpolatingFunction(double[] x, + double[] y, + double[][] f, + double[][] dFdX, + double[][] dFdY, + double[][] d2FdXdY) + throws DimensionMismatchException, + NoDataException, + NonMonotonicSequenceException { + final int xLen = x.length; + final int yLen = y.length; + + if (xLen == 0 || yLen == 0 || f.length == 0 || f[0].length == 0) { + throw new NoDataException(); + } + if (xLen != f.length) { + throw new DimensionMismatchException(xLen, f.length); + } + if (xLen != dFdX.length) { + throw new DimensionMismatchException(xLen, dFdX.length); + } + if (xLen != dFdY.length) { + throw new DimensionMismatchException(xLen, dFdY.length); + } + if (xLen != d2FdXdY.length) { + throw new DimensionMismatchException(xLen, d2FdXdY.length); + } + + MathArrays.checkOrder(x); + MathArrays.checkOrder(y); + + xval = x.clone(); + yval = y.clone(); + + final int lastI = xLen - 1; + final int lastJ = yLen - 1; + splines = new BicubicFunction[lastI][lastJ]; + + for (int i = 0; i < lastI; i++) { + if (f[i].length != yLen) { + throw new DimensionMismatchException(f[i].length, yLen); + } + if (dFdX[i].length != yLen) { + throw new DimensionMismatchException(dFdX[i].length, yLen); + } + if (dFdY[i].length != yLen) { + throw new DimensionMismatchException(dFdY[i].length, yLen); + } + if (d2FdXdY[i].length != yLen) { + throw new DimensionMismatchException(d2FdXdY[i].length, yLen); + } + final int ip1 = i + 1; + final double xR = xval[ip1] - xval[i]; + for (int j = 0; j < lastJ; j++) { + final int jp1 = j + 1; + final double yR = yval[jp1] - yval[j]; + final double xRyR = xR * yR; + final double[] beta = new double[] { + f[i][j], f[ip1][j], f[i][jp1], f[ip1][jp1], + dFdX[i][j] * xR, dFdX[ip1][j] * xR, dFdX[i][jp1] * xR, dFdX[ip1][jp1] * xR, + dFdY[i][j] * yR, dFdY[ip1][j] * yR, dFdY[i][jp1] * yR, dFdY[ip1][jp1] * yR, + d2FdXdY[i][j] * xRyR, d2FdXdY[ip1][j] * xRyR, d2FdXdY[i][jp1] * xRyR, d2FdXdY[ip1][jp1] * xRyR + }; + + splines[i][j] = new BicubicFunction(computeSplineCoefficients(beta)); + } + } + } + + /** + * {@inheritDoc} + */ + public double value(double x, double y) + throws OutOfRangeException { + final int i = searchIndex(x, xval); + final int j = searchIndex(y, yval); + + final double xN = (x - xval[i]) / (xval[i + 1] - xval[i]); + final double yN = (y - yval[j]) / (yval[j + 1] - yval[j]); + + return splines[i][j].value(xN, yN); + } + + /** + * Indicates whether a point is within the interpolation range. + * + * @param x First coordinate. + * @param y Second coordinate. + * @return {@code true} if (x, y) is a valid point. + */ + public boolean isValidPoint(double x, double y) { + if (x < xval[0] || + x > xval[xval.length - 1] || + y < yval[0] || + y > yval[yval.length - 1]) { + return false; + } else { + return true; + } + } + + /** + * @param c Coordinate. + * @param val Coordinate samples. + * @return the index in {@code val} corresponding to the interval + * containing {@code c}. + * @throws OutOfRangeException if {@code c} is out of the + * range defined by the boundary values of {@code val}. + */ + private int searchIndex(double c, double[] val) { + final int r = Arrays.binarySearch(val, c); + + if (r == -1 || + r == -val.length - 1) { + throw new OutOfRangeException(c, val[0], val[val.length - 1]); + } + + if (r < 0) { + // "c" in within an interpolation sub-interval: Return the + // index of the sample at the lower end of the sub-interval. + return -r - 2; + } + final int last = val.length - 1; + if (r == last) { + // "c" is the last sample of the range: Return the index + // of the sample at the lower end of the last sub-interval. + return last - 1; + } + + // "c" is another sample point. + return r; + } + + /** + * Compute the spline coefficients from the list of function values and + * function partial derivatives values at the four corners of a grid + * element. They must be specified in the following order: + * <ul> + * <li>f(0,0)</li> + * <li>f(1,0)</li> + * <li>f(0,1)</li> + * <li>f(1,1)</li> + * <li>f<sub>x</sub>(0,0)</li> + * <li>f<sub>x</sub>(1,0)</li> + * <li>f<sub>x</sub>(0,1)</li> + * <li>f<sub>x</sub>(1,1)</li> + * <li>f<sub>y</sub>(0,0)</li> + * <li>f<sub>y</sub>(1,0)</li> + * <li>f<sub>y</sub>(0,1)</li> + * <li>f<sub>y</sub>(1,1)</li> + * <li>f<sub>xy</sub>(0,0)</li> + * <li>f<sub>xy</sub>(1,0)</li> + * <li>f<sub>xy</sub>(0,1)</li> + * <li>f<sub>xy</sub>(1,1)</li> + * </ul> + * where the subscripts indicate the partial derivative with respect to + * the corresponding variable(s). + * + * @param beta List of function values and function partial derivatives + * values. + * @return the spline coefficients. + */ + private double[] computeSplineCoefficients(double[] beta) { + final double[] a = new double[NUM_COEFF]; + + for (int i = 0; i < NUM_COEFF; i++) { + double result = 0; + final double[] row = AINV[i]; + for (int j = 0; j < NUM_COEFF; j++) { + result += row[j] * beta[j]; + } + a[i] = result; + } + + return a; + } +} + +/** + * Bicubic function. + */ +class BicubicFunction implements BivariateFunction { + /** Number of points. */ + private static final short N = 4; + /** Coefficients */ + private final double[][] a; + + /** + * Simple constructor. + * + * @param coeff Spline coefficients. + */ + BicubicFunction(double[] coeff) { + a = new double[N][N]; + for (int j = 0; j < N; j++) { + final double[] aJ = a[j]; + for (int i = 0; i < N; i++) { + aJ[i] = coeff[i * N + j]; + } + } + } + + /** + * {@inheritDoc} + */ + public double value(double x, double y) { + if (x < 0 || x > 1) { + throw new OutOfRangeException(x, 0, 1); + } + if (y < 0 || y > 1) { + throw new OutOfRangeException(y, 0, 1); + } + + final double x2 = x * x; + final double x3 = x2 * x; + final double[] pX = {1, x, x2, x3}; + + final double y2 = y * y; + final double y3 = y2 * y; + final double[] pY = {1, y, y2, y3}; + + return apply(pX, pY, a); + } + + /** + * Compute the value of the bicubic polynomial. + * + * @param pX Powers of the x-coordinate. + * @param pY Powers of the y-coordinate. + * @param coeff Spline coefficients. + * @return the interpolated value. + */ + private double apply(double[] pX, double[] pY, double[][] coeff) { + double result = 0; + for (int i = 0; i < N; i++) { + final double r = MathArrays.linearCombination(coeff[i], pY); + result += r * pX[i]; + } + + return result; + } +} |