one (single)-sided fft and fft2

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Linan Xu
Linan Xu 2018-6-19
评论： David Goodmanson 2018-6-20
The solution of FFT is symmetric. I am wondering whether there is a built-in function to produce a one(single)-sided solution. One-dimensional transform is simple. How can we make a 2D FFT producing a single-sided solution?
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Linan Xu
Linan Xu 2018-6-20
I forgot that fft(a')' is not fft(a). I have fixed the function ifft_half.
function [s] = ifft_half(s,n,opt)
% Inputs:
% s: one-sided Fourier coefficients (frequency domain).
% opt: 'fftshift' or none
% Output:
% S: full signal in the time domain.
tmp=iscolumn(s);
if tmp==0
s=s';
end
if mod(n,2)==0 %even number
S=[s;conj(flip(s(2:end-1)))];
else % odd number
S=[s;conj(flip(s(2:end)))];
end
if tmp==0
S=S';
end
if nargin==2
s=ifft(S);
else
s=ifft(ifftshift(s));
end
end
David Goodmanson
David Goodmanson 2018-6-20
Since the intent was simply to transpose input s to a column vector without complex conjugation, it might be clearer later on to take your previous code and use s.' instead of s' in a couple of places.
fft2(rand(4,4)) or fft2(rand(5,5)) or fft2(rand(5,4)) shows that placement of the complex conjugates is not so easy in the 2d case.

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