All input options for fft so I can correctly do fft with respect to a single dimension in multidimensional array.

So I have a array A with dimensions [x y z t] of size [64 64 64 19] and I want to take the fft for every [x y z] position with respect to t. For this I thought I could evaluate B=fft(A, [], 4); taking the fft with respect to the fourth dimension. However if i then take for instance B(32,32,32,:) it is not the same as fft(A(32,32,32,:)). What am I doing wrong? Has it got to do with the [] input for fft? Nowhere in the documentation can I find how to use those brackets.

This is where Ive looked so far: http://www.mathworks.nl/help/matlab/ref/fft.html http://www.mathworks.nl/help/matlab/math/fast-fourier-transform-fft.html

Answer 1

[Matt J]

However if i then take for instance B(32,32,32,:) it is not the same as fft(A(32,32,32,:)). What am I doing wrong?

I can't reproduce this observation, I'm afraid. As an experiment, I have done

 A=rand(64,64,64,19);

 B=fft(A,[],4);

 C=fft(A(32,32,32,:));

Then at the command line, I find the agreement expected

      >> isequal(B(32,32,32,:),C)

      ans =

           1

[Lennart]

Hmm then my code must have an error somewhere else... strange. Ill check again. thanks anyways