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Java example source code file (TransformUtils.java)

This example Java source code file (TransformUtils.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

complex, dimensionmismatchexception, mathillegalargumentexception, powers_of_two, transformutils, util

The TransformUtils.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.transform;

import java.util.Arrays;

import org.apache.commons.math3.complex.Complex;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.MathIllegalArgumentException;
import org.apache.commons.math3.exception.util.LocalizedFormats;

/**
 * Useful functions for the implementation of various transforms.
 *
 * @since 3.0
 */
public class TransformUtils {
    /**
     * Table of the powers of 2 to facilitate binary search lookup.
     *
     * @see #exactLog2(int)
     */
    private static final int[] POWERS_OF_TWO = {
        0x00000001, 0x00000002, 0x00000004, 0x00000008, 0x00000010, 0x00000020,
        0x00000040, 0x00000080, 0x00000100, 0x00000200, 0x00000400, 0x00000800,
        0x00001000, 0x00002000, 0x00004000, 0x00008000, 0x00010000, 0x00020000,
        0x00040000, 0x00080000, 0x00100000, 0x00200000, 0x00400000, 0x00800000,
        0x01000000, 0x02000000, 0x04000000, 0x08000000, 0x10000000, 0x20000000,
        0x40000000
    };

    /** Private constructor. */
    private TransformUtils() {
        super();
    }

    /**
     * Multiply every component in the given real array by the
     * given real number. The change is made in place.
     *
     * @param f the real array to be scaled
     * @param d the real scaling coefficient
     * @return a reference to the scaled array
     */
    public static double[] scaleArray(double[] f, double d) {

        for (int i = 0; i < f.length; i++) {
            f[i] *= d;
        }
        return f;
    }

    /**
     * Multiply every component in the given complex array by the
     * given real number. The change is made in place.
     *
     * @param f the complex array to be scaled
     * @param d the real scaling coefficient
     * @return a reference to the scaled array
     */
    public static Complex[] scaleArray(Complex[] f, double d) {

        for (int i = 0; i < f.length; i++) {
            f[i] = new Complex(d * f[i].getReal(), d * f[i].getImaginary());
        }
        return f;
    }


    /**
     * Builds a new two dimensional array of {@code double} filled with the real
     * and imaginary parts of the specified {@link Complex} numbers. In the
     * returned array {@code dataRI}, the data is laid out as follows
     * <ul>
     * <li>{@code dataRI[0][i] = dataC[i].getReal()},
     * <li>{@code dataRI[1][i] = dataC[i].getImaginary()}.
     * </ul>
     *
     * @param dataC the array of {@link Complex} data to be transformed
     * @return a two dimensional array filled with the real and imaginary parts
     *   of the specified complex input
     */
    public static double[][] createRealImaginaryArray(final Complex[] dataC) {
        final double[][] dataRI = new double[2][dataC.length];
        final double[] dataR = dataRI[0];
        final double[] dataI = dataRI[1];
        for (int i = 0; i < dataC.length; i++) {
            final Complex c = dataC[i];
            dataR[i] = c.getReal();
            dataI[i] = c.getImaginary();
        }
        return dataRI;
    }

    /**
     * Builds a new array of {@link Complex} from the specified two dimensional
     * array of real and imaginary parts. In the returned array {@code dataC},
     * the data is laid out as follows
     * <ul>
     * <li>{@code dataC[i].getReal() = dataRI[0][i]},
     * <li>{@code dataC[i].getImaginary() = dataRI[1][i]}.
     * </ul>
     *
     * @param dataRI the array of real and imaginary parts to be transformed
     * @return an array of {@link Complex} with specified real and imaginary parts.
     * @throws DimensionMismatchException if the number of rows of the specified
     *   array is not two, or the array is not rectangular
     */
    public static Complex[] createComplexArray(final double[][] dataRI)
        throws DimensionMismatchException{

        if (dataRI.length != 2) {
            throw new DimensionMismatchException(dataRI.length, 2);
        }
        final double[] dataR = dataRI[0];
        final double[] dataI = dataRI[1];
        if (dataR.length != dataI.length) {
            throw new DimensionMismatchException(dataI.length, dataR.length);
        }

        final int n = dataR.length;
        final Complex[] c = new Complex[n];
        for (int i = 0; i < n; i++) {
            c[i] = new Complex(dataR[i], dataI[i]);
        }
        return c;
    }


    /**
     * Returns the base-2 logarithm of the specified {@code int}. Throws an
     * exception if {@code n} is not a power of two.
     *
     * @param n the {@code int} whose base-2 logarithm is to be evaluated
     * @return the base-2 logarithm of {@code n}
     * @throws MathIllegalArgumentException if {@code n} is not a power of two
     */
    public static int exactLog2(final int n)
        throws MathIllegalArgumentException {

        int index = Arrays.binarySearch(TransformUtils.POWERS_OF_TWO, n);
        if (index < 0) {
            throw new MathIllegalArgumentException(
                    LocalizedFormats.NOT_POWER_OF_TWO_CONSIDER_PADDING,
                    Integer.valueOf(n));
        }
        return index;
    }
}

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