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Diffstat (limited to 'src/main/java/org/apache/commons/math/analysis/interpolation/BicubicSplineInterpolator.java')
-rw-r--r-- | src/main/java/org/apache/commons/math/analysis/interpolation/BicubicSplineInterpolator.java | 145 |
1 files changed, 145 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/math/analysis/interpolation/BicubicSplineInterpolator.java b/src/main/java/org/apache/commons/math/analysis/interpolation/BicubicSplineInterpolator.java new file mode 100644 index 0000000..42f73c8 --- /dev/null +++ b/src/main/java/org/apache/commons/math/analysis/interpolation/BicubicSplineInterpolator.java @@ -0,0 +1,145 @@ +/* + * 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.interpolation; + +import org.apache.commons.math.DimensionMismatchException; +import org.apache.commons.math.MathException; +import org.apache.commons.math.analysis.UnivariateRealFunction; +import org.apache.commons.math.analysis.polynomials.PolynomialSplineFunction; +import org.apache.commons.math.exception.NoDataException; +import org.apache.commons.math.util.MathUtils; + +/** + * Generates a bicubic interpolating function. + * + * @version $Revision: 980944 $ $Date: 2010-07-30 22:31:11 +0200 (ven. 30 juil. 2010) $ + * @since 2.2 + */ +public class BicubicSplineInterpolator + implements BivariateRealGridInterpolator { + /** + * {@inheritDoc} + */ + public BicubicSplineInterpolatingFunction interpolate(final double[] xval, + final double[] yval, + final double[][] fval) + throws MathException, IllegalArgumentException { + if (xval.length == 0 || yval.length == 0 || fval.length == 0) { + throw new NoDataException(); + } + if (xval.length != fval.length) { + throw new DimensionMismatchException(xval.length, fval.length); + } + + MathUtils.checkOrder(xval); + MathUtils.checkOrder(yval); + + final int xLen = xval.length; + final int yLen = yval.length; + + // Samples (first index is y-coordinate, i.e. subarray variable is x) + // 0 <= i < xval.length + // 0 <= j < yval.length + // fX[j][i] = f(xval[i], yval[j]) + final double[][] fX = new double[yLen][xLen]; + for (int i = 0; i < xLen; i++) { + if (fval[i].length != yLen) { + throw new DimensionMismatchException(fval[i].length, yLen); + } + + for (int j = 0; j < yLen; j++) { + fX[j][i] = fval[i][j]; + } + } + + final SplineInterpolator spInterpolator = new SplineInterpolator(); + + // For each line y[j] (0 <= j < yLen), construct a 1D spline with + // respect to variable x + final PolynomialSplineFunction[] ySplineX = new PolynomialSplineFunction[yLen]; + for (int j = 0; j < yLen; j++) { + ySplineX[j] = spInterpolator.interpolate(xval, fX[j]); + } + + // For each line x[i] (0 <= i < xLen), construct a 1D spline with + // respect to variable y generated by array fY_1[i] + final PolynomialSplineFunction[] xSplineY = new PolynomialSplineFunction[xLen]; + for (int i = 0; i < xLen; i++) { + xSplineY[i] = spInterpolator.interpolate(yval, fval[i]); + } + + // Partial derivatives with respect to x at the grid knots + final double[][] dFdX = new double[xLen][yLen]; + for (int j = 0; j < yLen; j++) { + final UnivariateRealFunction f = ySplineX[j].derivative(); + for (int i = 0; i < xLen; i++) { + dFdX[i][j] = f.value(xval[i]); + } + } + + // Partial derivatives with respect to y at the grid knots + final double[][] dFdY = new double[xLen][yLen]; + for (int i = 0; i < xLen; i++) { + final UnivariateRealFunction f = xSplineY[i].derivative(); + for (int j = 0; j < yLen; j++) { + dFdY[i][j] = f.value(yval[j]); + } + } + + // Cross partial derivatives + final double[][] d2FdXdY = new double[xLen][yLen]; + for (int i = 0; i < xLen ; i++) { + final int nI = nextIndex(i, xLen); + final int pI = previousIndex(i); + for (int j = 0; j < yLen; j++) { + final int nJ = nextIndex(j, yLen); + final int pJ = previousIndex(j); + d2FdXdY[i][j] = (fval[nI][nJ] - fval[nI][pJ] - + fval[pI][nJ] + fval[pI][pJ]) / + ((xval[nI] - xval[pI]) * (yval[nJ] - yval[pJ])); + } + } + + // Create the interpolating splines + return new BicubicSplineInterpolatingFunction(xval, yval, fval, + dFdX, dFdY, d2FdXdY); + } + + /** + * Compute the next index of an array, clipping if necessary. + * It is assumed (but not checked) that {@code i} is larger than or equal to 0}. + * + * @param i Index + * @param max Upper limit of the array + * @return the next index + */ + private int nextIndex(int i, int max) { + final int index = i + 1; + return index < max ? index : index - 1; + } + /** + * Compute the previous index of an array, clipping if necessary. + * It is assumed (but not checked) that {@code i} is smaller than the size of the array. + * + * @param i Index + * @return the previous index + */ + private int previousIndex(int i) { + final int index = i - 1; + return index >= 0 ? index : 0; + } +} |