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Re: Problems with FFT and IFFT
From: |
Sascha Berkenkamp |
Subject: |
Re: Problems with FFT and IFFT |
Date: |
Tue, 28 Feb 2006 20:13:55 +0100 |
User-agent: |
Mutt/1.5.11+cvs20060126 |
* John W. Eaton <address@hidden> [28.02.2006 17:52]:
> What kind of hardware? I see imaginary parts, but all less than
> eps.
I use x86, Pentium Centrino 1.6 GHZ, Octave from Debian Etch
> octave_config_info ("FFTW_LIBS")
octave:21> octave_config_info ("FFTW_LIBS")
ans = -lfftw3
Some of the values are greater than eps
octave:22> eps
eps = 2.2204e-16
octave:23> imag(x2)
ans =
Columns 1 through 8:
0.0000e+00 3.5175e-17 1.1061e-16 6.6476e-17 2.1199e-16
-2.4203e-17 2.0483e-16 2.5125e-17
Columns 9 through 16:
-1.9568e-16 -1.3944e-16 1.0716e-16 -3.9844e-17 -9.0520e-17
2.5194e-16 1.0905e-18 -1.6137e-16
Columns 17 through 24:
-5.0008e-17 3.7599e-17 6.8233e-17 -7.3672e-17 2.1367e-16
3.0135e-17 -1.1130e-16 -4.6083e-17
Columns 25 through 32:
2.5070e-17 -3.2290e-16 3.4958e-17 -8.9096e-17 -1.4279e-16
1.3788e-16 5.2801e-17 2.9702e-17
Columns 33 through 40:
-1.7758e-16 7.6944e-19 2.3255e-16 1.5679e-16 -2.0947e-17
2.0342e-16 -1.9384e-16 -1.2851e-16
Columns 41 through 48:
1.9127e-16 3.5370e-17 -2.0086e-18 1.1304e-17 1.3220e-16
-4.5291e-18 -9.9986e-17 -1.6011e-16
Columns 49 through 56:
-3.9844e-17 6.3589e-17 -1.0564e-16 -3.0778e-17 1.4462e-16
-4.0874e-17 8.2015e-17 1.7684e-16
Columns 57 through 64:
-5.7632e-17 5.4866e-18 -4.8098e-17 -3.8728e-17 -8.8911e-17
9.4316e-17 -7.3907e-18 -9.4484e-18
Columns 65 through 72:
-3.2554e-16 0.0000e+00 -1.1167e-16 -1.0787e-16 3.0963e-17
7.2214e-17 1.0869e-16 2.7486e-17
Columns 73 through 80:
-3.6979e-17 -2.3208e-17 1.7468e-17 -9.6645e-17 2.5633e-16
-3.9809e-17 1.2463e-17 3.3627e-17
Columns 81 through 88:
7.7609e-17 -8.7662e-17 2.7347e-17 3.0778e-17 -4.0610e-17
5.7000e-17 1.9934e-16 -2.0947e-17
Columns 89 through 96:
-2.4703e-16 4.5723e-17 1.1818e-16 8.1443e-18 -4.6655e-18
1.5679e-16 7.6130e-17 -4.0610e-17
Columns 97 through 101:
-1.9494e-16 -1.0285e-16 -8.9592e-17 -1.5124e-16 -6.7643e-17
But I think that the values before the transformation and after the
retransformation are not the same:
octave:27> real(x)
Columns 1 through 12:
0.00000 0.58779 0.95106 0.95106 0.58779 0.00000 -0.58779
-0.95106 -0.95106 -0.58779 -0.00000 0.58779
Columns 13 through 24:
0.95106 0.95106 0.58779 0.00000 -0.58779 -0.95106 -0.95106
-0.58779 -0.00000 0.58779 0.95106 0.95106
....
octave:27> real(x2)
Columns 1 through 8:
4.6168e-17 5.8779e-01 9.5106e-01 9.5106e-01 5.8779e-01
-7.0351e-17 -5.8779e-01 -9.5106e-01
Columns 9 through 16:
-9.5106e-01 -5.8779e-01 -3.1658e-16 5.8779e-01 9.5106e-01
9.5106e-01 5.8779e-01 -3.5175e-17
Columns 17 through 24:
-5.8779e-01 -9.5106e-01 -9.5106e-01 -5.8779e-01 -2.1105e-16
5.8779e-01 9.5106e-01 9.5106e-01
Must I set all values smaller than eps to zeros?
Sascha
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- Problems with FFT and IFFT, Sascha Berkenkamp, 2006/02/28
- Re: Problems with FFT and IFFT, Keith Goodman, 2006/02/28
- Re: Problems with FFT and IFFT, Keith Goodman, 2006/02/28
- Re: Problems with FFT and IFFT, John W. Eaton, 2006/02/28
- Re: Problems with FFT and IFFT, Dmitri A. Sergatskov, 2006/02/28
- Re: Problems with FFT and IFFT,
Sascha Berkenkamp <=
- Re: Problems with FFT and IFFT, John W. Eaton, 2006/02/28
- Re: Problems with FFT and IFFT, Joe Koski, 2006/02/28
- Re: Problems with FFT and IFFT, Quentin Spencer, 2006/02/28
- Re: Problems with FFT and IFFT, Joe Koski, 2006/02/28
- Re: Problems with FFT and IFFT, Bill Denney, 2006/02/28
- Re: Problems with FFT and IFFT, Steve C. Thompson, 2006/02/28
- RE: Problems with FFT and IFFT, Frank Palazzolo, 2006/02/28
Re: Problems with FFT and IFFT, Joe Koski, 2006/02/28