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Java example source code file (PiecewiseBicubicSplineInterpolatingFunction.java)

This example Java source code file (PiecewiseBicubicSplineInterpolatingFunction.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

akimasplineinterpolator, bivariatefunction, dimensionmismatchexception, insufficientdataexception, min_num_points, nodataexception, nonmonotonicsequenceexception, nullargumentexception, outofrangeexception, piecewisebicubicsplineinterpolatingfunction, polynomialsplinefunction, util

The PiecewiseBicubicSplineInterpolatingFunction.java Java example source code

/*
 * 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.analysis.polynomials.PolynomialSplineFunction;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.InsufficientDataException;
import org.apache.commons.math3.exception.NoDataException;
import org.apache.commons.math3.exception.NullArgumentException;
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://www.paulinternet.nl/?page=bicubic">bicubic spline
 * interpolation.
 * This implementation currently uses {@link AkimaSplineInterpolator} as the
 * underlying one-dimensional interpolator, which requires 5 sample points;
 * insufficient data will raise an exception when the
 * {@link #value(double,double) value} method is called.
 *
 * @since 3.4
 */
public class PiecewiseBicubicSplineInterpolatingFunction
    implements BivariateFunction {
    /** The minimum number of points that are needed to compute the function. */
    private static final int MIN_NUM_POINTS = 5;
    /** 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 double[][] fval;

    /**
     * @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. the expected number
     *        of elements.
     * @throws NonMonotonicSequenceException if {@code x} or {@code y} are not
     *         strictly increasing.
     * @throws NullArgumentException if any of the arguments are null
     * @throws NoDataException if any of the arrays has zero length.
     * @throws DimensionMismatchException if the length of x and y don't match the row, column
     *         height of f
     */
    public PiecewiseBicubicSplineInterpolatingFunction(double[] x,
                                                       double[] y,
                                                       double[][] f)
        throws DimensionMismatchException,
               NullArgumentException,
               NoDataException,
               NonMonotonicSequenceException {
        if (x == null ||
            y == null ||
            f == null ||
            f[0] == null) {
            throw new NullArgumentException();
        }

        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 < MIN_NUM_POINTS ||
            yLen < MIN_NUM_POINTS ||
            f.length < MIN_NUM_POINTS ||
            f[0].length < MIN_NUM_POINTS) {
            throw new InsufficientDataException();
        }

        if (xLen != f.length) {
            throw new DimensionMismatchException(xLen, f.length);
        }

        if (yLen != f[0].length) {
            throw new DimensionMismatchException(yLen, f[0].length);
        }

        MathArrays.checkOrder(x);
        MathArrays.checkOrder(y);

        xval = x.clone();
        yval = y.clone();
        fval = f.clone();
    }

    /**
     * {@inheritDoc}
     */
    public double value(double x,
                        double y)
        throws OutOfRangeException {
        final AkimaSplineInterpolator interpolator = new AkimaSplineInterpolator();
        final int offset = 2;
        final int count = offset + 3;
        final int i = searchIndex(x, xval, offset, count);
        final int j = searchIndex(y, yval, offset, count);

        final double xArray[] = new double[count];
        final double yArray[] = new double[count];
        final double zArray[] = new double[count];
        final double interpArray[] = new double[count];

        for (int index = 0; index < count; index++) {
            xArray[index] = xval[i + index];
            yArray[index] = yval[j + index];
        }

        for (int zIndex = 0; zIndex < count; zIndex++) {
            for (int index = 0; index < count; index++) {
                zArray[index] = fval[i + index][j + zIndex];
            }
            final PolynomialSplineFunction spline = interpolator.interpolate(xArray, zArray);
            interpArray[zIndex] = spline.value(x);
        }

        final PolynomialSplineFunction spline = interpolator.interpolate(yArray, interpArray);

        double returnValue = spline.value(y);

        return returnValue;
    }

    /**
     * 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.
     * @since 3.3
     */
    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.
     * @param offset how far back from found value to offset for querying
     * @param count total number of elements forward from beginning that will be
     *        queried
     * @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,
                            int offset,
                            int count) {
        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, which returns
            // negative
            // need to remove the negative sign for consistency
            r = -r - offset - 1;
        } else {
            r -= offset;
        }

        if (r < 0) {
            r = 0;
        }

        if ((r + count) >= val.length) {
            // "c" is the last sample of the range: Return the index
            // of the sample at the lower end of the last sub-interval.
            r = val.length - count;
        }

        return r;
    }
}

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