| /* |
| * 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.math4.transform; |
| |
| import java.util.function.DoubleUnaryOperator; |
| |
| import org.apache.commons.numbers.complex.Complex; |
| |
| /** |
| * Useful functions for the implementation of various transforms. |
| * Class is package-private (for internal use only). |
| */ |
| final class TransformUtils { |
| /** Number of array slots: 1 for "real" parts 1 for "imaginary" parts. */ |
| private static final int NUM_PARTS = 2; |
| |
| /** Utility class. */ |
| private TransformUtils() {} |
| |
| /** |
| * Multiply every component in the given real array by the |
| * given real number. The change is made in place. |
| * |
| * @param f Array to be scaled. |
| * @param d Scaling coefficient. |
| * @return a reference to the scaled array. |
| */ |
| static double[] scaleInPlace(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 Array to be scaled. |
| * @param d Scaling coefficient. |
| * @return the scaled array. |
| */ |
| static Complex[] scaleInPlace(Complex[] f, double d) { |
| for (int i = 0; i < f.length; i++) { |
| f[i] = Complex.ofCartesian(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 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. |
| */ |
| static double[][] createRealImaginary(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 Array of real and imaginary parts to be transformed. |
| * @return a {@link Complex} array. |
| * @throws IllegalArgumentException if the number of rows of the specified |
| * array is not two, or the array is not rectangular. |
| */ |
| static Complex[] createComplex(final double[][] dataRI) { |
| if (dataRI.length != NUM_PARTS) { |
| throw new TransformException(TransformException.SIZE_MISMATCH, |
| dataRI.length, NUM_PARTS); |
| } |
| final double[] dataR = dataRI[0]; |
| final double[] dataI = dataRI[1]; |
| if (dataR.length != dataI.length) { |
| throw new TransformException(TransformException.SIZE_MISMATCH, |
| dataI.length, dataR.length); |
| } |
| |
| final int n = dataR.length; |
| final Complex[] c = new Complex[n]; |
| for (int i = 0; i < n; i++) { |
| c[i] = Complex.ofCartesian(dataR[i], dataI[i]); |
| } |
| return c; |
| } |
| |
| /** |
| * Samples the specified univariate real function on the specified interval. |
| * <p> |
| * The interval is divided equally into {@code n} sections and sample points |
| * are taken from {@code min} to {@code max - (max - min) / n}; therefore |
| * {@code f} is not sampled at the upper bound {@code max}.</p> |
| * |
| * @param f Function to be sampled |
| * @param min Lower bound of the interval (included). |
| * @param max Upper bound of the interval (excluded). |
| * @param n Number of sample points. |
| * @return the array of samples. |
| * @throws IllegalArgumentException if the lower bound {@code min} is |
| * greater than, or equal to the upper bound {@code max}, if the number |
| * of sample points {@code n} is negative. |
| */ |
| static double[] sample(DoubleUnaryOperator f, |
| double min, |
| double max, |
| int n) { |
| if (n <= 0) { |
| throw new TransformException(TransformException.NOT_STRICTLY_POSITIVE, |
| Integer.valueOf(n)); |
| } |
| if (min >= max) { |
| throw new TransformException(TransformException.TOO_LARGE, min, max); |
| } |
| |
| final double[] s = new double[n]; |
| final double h = (max - min) / n; |
| for (int i = 0; i < n; i++) { |
| s[i] = f.applyAsDouble(min + i * h); |
| } |
| return s; |
| } |
| } |