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