MATLAB: Query on DFT plotting

Question

x_mags=abs(fft(x));

plot(x_mags);

xlabel('DFT bins');

ylabel('magnitude');

%plotting the DFT(norm freq)

num_bins=length(x_mags);

plot([0:1/(num_bins/2 -1):1], x_mags(1:num_bins/2));

xlabel('norm frequency (\pi rads/sample)');

ylabel('magnitude');

so the text i bolded and underlined, why are the limits in plot in such way?

is there any specific reason?

Answer 1

It is plotting only the first half of the fft result ‘x_mags’ from 0 to π radians. This is the usual approach, since ‘x_mags’ is actually symmetrical, with the second half being the complex conjugate of the first half. (There is usuallny no reason to plot both halves, unless you are using fftshift and plotting from to π in this instance. That is not the situation here.)