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FFT single sided spectrum imagesc plot

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Farai Mahachi
Farai Mahachi 2019-6-20
关闭： MATLAB Answer Bot 2021-8-20
Hi guys
I have a matrix where I have performed an FFT operation, and I can view it using the imagesc function. However, I am seeing the negative spectrum as well, as shown in the figure below.
what_i_have.png
I have tried the using documentation of the single spectrum FFT from the web page but its not giving me what I want, as shown below:
% Script 1
% Try again removing negative spectrum
L = length(tmp);
P2 = abs(tmp/L);
P1 = P2(1:L/2+1);
P1(2:end-1) = 2*P1(2:end-1);
figure
imagesc(P1)
% Script 2
% here is another code snippet for removing the negative spectrum
X_mags = abs(tmp);
N_2 = ceil(L/2);
figure
imagesc(X_mags(1:N_2))
The output of the two separate scripts is shown below: definitely not what I want.
not_what_i_want.png
How can I only plot the positive spectrum of the matrix - with out using the fftshift?
Regards,

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