for loop for 15x2045 matrix

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Sag 2016-2-16

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评论： Sag 2016-2-18

I am trying to run fft function for every row of 15x2045 matrix. 13 out of 15 rows have NaN as the last element (2045th element) How I can do it? so far I have tried this:

 for k = 1:length(Final) %Final is 15x2045 matrix (I have converted a cell to this matrix)
    HH = fft(Final{k},NFFT)/L;
    power=(2*abs(HH(1:NFFT/2+1)));
 end
 %error I get is:Cell contents reference from a non-cell array object.

I appreciate any help, Thanks!

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Walter Roberson 2016-2-17

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https://ww2.mathworks.cn/matlabcentral/answers/268504-for-loop-for-15x2045-matrix#answer_210095

编辑：Walter Roberson 2016-2-17

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 for k = 1 : size(Final,1) %Final is 15x2045 matrix (I have converted a cell to this matrix)
    HH(k,:) = fft(Final(k,:),NFFT)/L;
    Fpower(k,:) = (2*abs(HH(k,1:NFFT/2+1)));
 end

I renamed power to Fpower to avoid interfering with the MATLAB function named power (which is more commonly known as the .^ operator)

Note: you do not need to do this column by column. You can vectorize it as

HH = fft(Final, NFFT, 2)./L;
Fpower = 2 * abs(HH(:,1:NFFT/2+1));

You need to expect NaN as the result for any row of Final that has a NaN in it. NaN "pollutes" or "taints" any calculation that it takes part in. Think of NaN as meaning "Any calculation involving this value is an error!". FFT has to determine contributions at various frequencies and with a data value that is error, it is not possible to determine the contributions.

If you are using NaN as a place-holder indicating that the data is missing or unknown and that the calculation should try to proceed without that data point, then FFT is the wrong calculation routine to use. You need to use a non-uniform FFT for such a situation. See http://www.mathworks.com/matlabcentral/fileexchange/25135-nufft--nfft--usfft and http://www.mathworks.com/matlabcentral/answers/113873-non-uniform-fft-with-matlab

Sag 2016-2-18