Java tutorial
/* * 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. * * @version $Id: TransformUtils.java 1385310 2012-09-16 16:32:10Z tn $ * @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> * <li>{@code dataRI[1][i] = dataC[i].getImaginary()}.</li> * </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> * <li>{@code dataC[i].getImaginary() = dataRI[1][i]}.</li> * </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; } }