// // Math.NET Numerics, part of the Math.NET Project // http://numerics.mathdotnet.com // http://github.com/mathnet/mathnet-numerics // // Copyright (c) 2009-2014 Math.NET // // Permission is hereby granted, free of charge, to any person // obtaining a copy of this software and associated documentation // files (the "Software"), to deal in the Software without // restriction, including without limitation the rights to use, // copy, modify, merge, publish, distribute, sublicense, and/or sell // copies of the Software, and to permit persons to whom the // Software is furnished to do so, subject to the following // conditions: // // The above copyright notice and this permission notice shall be // included in all copies or substantial portions of the Software. // // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES // OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT // HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, // WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING // FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR // OTHER DEALINGS IN THE SOFTWARE. // using System; namespace IStation.Numerics.IntegralTransforms { /// /// Fast (FHT) Implementation of the Discrete Hartley Transform (DHT). /// public static partial class Hartley { /// /// Naive forward DHT, useful e.g. to verify faster algorithms. /// /// Time-space sample vector. /// Hartley Transform Convention Options. /// Corresponding frequency-space vector. public static double[] NaiveForward(double[] timeSpace, HartleyOptions options) { var frequencySpace = Naive(timeSpace); ForwardScaleByOptions(options, frequencySpace); return frequencySpace; } /// /// Naive inverse DHT, useful e.g. to verify faster algorithms. /// /// Frequency-space sample vector. /// Hartley Transform Convention Options. /// Corresponding time-space vector. public static double[] NaiveInverse(double[] frequencySpace, HartleyOptions options) { var timeSpace = Naive(frequencySpace); InverseScaleByOptions(options, timeSpace); return timeSpace; } /// /// Rescale FFT-the resulting vector according to the provided convention options. /// /// Fourier Transform Convention Options. /// Sample Vector. static void ForwardScaleByOptions(HartleyOptions options, double[] samples) { if ((options & HartleyOptions.NoScaling) == HartleyOptions.NoScaling || (options & HartleyOptions.AsymmetricScaling) == HartleyOptions.AsymmetricScaling) { return; } var scalingFactor = Math.Sqrt(1.0/samples.Length); for (int i = 0; i < samples.Length; i++) { samples[i] *= scalingFactor; } } /// /// Rescale the iFFT-resulting vector according to the provided convention options. /// /// Fourier Transform Convention Options. /// Sample Vector. static void InverseScaleByOptions(HartleyOptions options, double[] samples) { if ((options & HartleyOptions.NoScaling) == HartleyOptions.NoScaling) { return; } var scalingFactor = 1.0/samples.Length; if ((options & HartleyOptions.AsymmetricScaling) != HartleyOptions.AsymmetricScaling) { scalingFactor = Math.Sqrt(scalingFactor); } for (int i = 0; i < samples.Length; i++) { samples[i] *= scalingFactor; } } } }