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[Octave-bug-tracker] [bug #45932] ifft(fft(x)) is not real for x real
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From: |
Mike Miller |
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Subject: |
[Octave-bug-tracker] [bug #45932] ifft(fft(x)) is not real for x real |
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Date: |
Sat, 12 Sep 2015 00:40:57 +0000 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Firefox/38.0 Iceweasel/38.2.1 |
Update of bug #45932 (project octave):
Status: None => Confirmed
Release: 4.0.0 => dev
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Follow-up Comment #1:
No, there is no detection that the input is conjugate symmetric. If the (ifft)
input array is complex, then a complex-to-complex inverse FFT is done and the
output is complex.
It might make sense to add some heuristics to detect some of the symmetric
special cases, if not to choose a different function then to at least clean up
the round-off errors in the output.
Also note the roundoff error in double vs single:
>> max (abs (imag (ifft (fft (rand (101, 1, "double"))))))
ans = 1.2884e-16
>> max (abs (imag (ifft (fft (rand (101, 1, "single"))))))
ans = 6.0432e-08
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Reply to this item at:
<http://savannah.gnu.org/bugs/?45932>
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