[2563] | 1 | /*************************************************************************
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| 2 | Copyright (c) 2009, Sergey Bochkanov (ALGLIB project).
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| 3 |
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| 4 | >>> SOURCE LICENSE >>>
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| 5 | This program is free software; you can redistribute it and/or modify
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| 6 | it under the terms of the GNU General Public License as published by
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| 7 | the Free Software Foundation (www.fsf.org); either version 2 of the
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| 8 | License, or (at your option) any later version.
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| 9 |
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| 10 | This program is distributed in the hope that it will be useful,
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| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 13 | GNU General Public License for more details.
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| 14 |
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| 15 | A copy of the GNU General Public License is available at
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| 16 | http://www.fsf.org/licensing/licenses
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| 17 |
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| 18 | >>> END OF LICENSE >>>
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| 19 | *************************************************************************/
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| 20 |
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| 21 | using System;
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| 22 |
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| 23 | namespace alglib
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| 24 | {
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| 25 | public class fht
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| 26 | {
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| 27 | /*************************************************************************
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| 28 | 1-dimensional Fast Hartley Transform.
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| 29 |
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| 30 | Algorithm has O(N*logN) complexity for any N (composite or prime).
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| 31 |
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| 32 | INPUT PARAMETERS
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| 33 | A - array[0..N-1] - real function to be transformed
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| 34 | N - problem size
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| 35 |
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| 36 | OUTPUT PARAMETERS
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| 37 | A - FHT of a input array, array[0..N-1],
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| 38 | A_out[k] = sum(A_in[j]*(cos(2*pi*j*k/N)+sin(2*pi*j*k/N)), j=0..N-1)
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| 39 |
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| 40 |
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| 41 | -- ALGLIB --
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| 42 | Copyright 04.06.2009 by Bochkanov Sergey
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| 43 | *************************************************************************/
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| 44 | public static void fhtr1d(ref double[] a,
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| 45 | int n)
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| 46 | {
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| 47 | ftbase.ftplan plan = new ftbase.ftplan();
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| 48 | int i = 0;
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| 49 | AP.Complex[] fa = new AP.Complex[0];
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| 50 |
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| 51 | System.Diagnostics.Debug.Assert(n>0, "FHTR1D: incorrect N!");
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| 52 |
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| 53 | //
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| 54 | // Special case: N=1, FHT is just identity transform.
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| 55 | // After this block we assume that N is strictly greater than 1.
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| 56 | //
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| 57 | if( n==1 )
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| 58 | {
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| 59 | return;
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| 60 | }
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| 61 |
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| 62 | //
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| 63 | // Reduce FHt to real FFT
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| 64 | //
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| 65 | fft.fftr1d(ref a, n, ref fa);
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| 66 | for(i=0; i<=n-1; i++)
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| 67 | {
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| 68 | a[i] = fa[i].x-fa[i].y;
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| 69 | }
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| 70 | }
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| 71 |
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| 72 |
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| 73 | /*************************************************************************
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| 74 | 1-dimensional inverse FHT.
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| 75 |
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| 76 | Algorithm has O(N*logN) complexity for any N (composite or prime).
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| 77 |
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| 78 | INPUT PARAMETERS
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| 79 | A - array[0..N-1] - complex array to be transformed
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| 80 | N - problem size
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| 81 |
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| 82 | OUTPUT PARAMETERS
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| 83 | A - inverse FHT of a input array, array[0..N-1]
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| 84 |
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| 85 |
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| 86 | -- ALGLIB --
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| 87 | Copyright 29.05.2009 by Bochkanov Sergey
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| 88 | *************************************************************************/
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| 89 | public static void fhtr1dinv(ref double[] a,
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| 90 | int n)
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| 91 | {
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| 92 | int i = 0;
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| 93 |
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| 94 | System.Diagnostics.Debug.Assert(n>0, "FHTR1DInv: incorrect N!");
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| 95 |
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| 96 | //
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| 97 | // Special case: N=1, iFHT is just identity transform.
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| 98 | // After this block we assume that N is strictly greater than 1.
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| 99 | //
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| 100 | if( n==1 )
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| 101 | {
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| 102 | return;
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| 103 | }
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| 104 |
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| 105 | //
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| 106 | // Inverse FHT can be expressed in terms of the FHT as
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| 107 | //
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| 108 | // invfht(x) = fht(x)/N
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| 109 | //
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| 110 | fhtr1d(ref a, n);
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| 111 | for(i=0; i<=n-1; i++)
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| 112 | {
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| 113 | a[i] = a[i]/n;
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| 114 | }
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| 115 | }
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| 116 | }
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| 117 | }
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