fft(single) is giving inconsistent results

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Jeremy
Jeremy 2013-10-4
评论： Walter Roberson 2013-10-4
I have found that if I have an array of singles and I want to run it through fft so the transform is performed independently for each column, I get a different answer if I add on additional columns. I haven't been able to reproduce using random inputs, but i did save my inputs out from my workspace so the issue can be reproduced. the input time histories are attached.
I basically have a 10000x20 array of single precision, real numbers. If I add on an additional 10 columns of single precision, real numbers and run it through fft, I get a different result than if I just run the 20 columns through fft. There seems to be some interaction between the columns during the calculation, and the transform should definitely be performed independently for each channel.
I am running on 2012b 64-bit, I see the same result on 2010b 64-bit and 2012b 32-bit but NOT on 2010b 32-bit
load('fft vars.mat');
xxx=[bData mData];
isequal(bData(:,2),xxx(:,2))
f1=fft(xxx,[],1);
f2=fft(bData);
f1(591,2)
f2(591,2)
%what?!!
ans =
1
ans =
-40.3370 -39.9248i
ans =
-38.6038 -39.4498i

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