Initial Commit.

Functions/00. General/gen_freqgrid.m

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+function freq_grid = gen_freqgrid(N, Fs, opt)
+% gen_freqgrid   Generate frequency grid
+%   freq_grid = gen_freqgrid(N, Fs, opt) generate an N point
+%   frequency grid according to sample rate Fs. This grid matches
+%   the operation used in fftshift(opt = 1) or not(opt = 0).
+%
+%   % Example:
+%   %   Create a 16 point frequency grid for a sample rate of 10 
+%   %   Hz used in fftshift.
+%   
+%   freq_grid = gen_freqgrid(16, 10, 1)
+    
+% set 'CenterDC' in psdfreqvec to true preserves Nyquist point,
+% which does not match our processing to the data since we use
+% fftshift.
+
+% adopted from psdfreqvec 
+
+%% Checking 'opt' in input
+    if ~(opt == 0 || opt == 1)
+        disp('Option must be 0(No fftshift) or 1(fftshift)');
+        return;
+    end
+
+%% Generating freqeuncy grid
+    % freq_grid = fftshift(psdfreqvec(...
+    %     'Npts',N,'Fs',Fs,'Range','whole'));
+    freq_res = Fs/N;
+    freq_grid = (0:N-1).'*freq_res;
+
+    if opt == 1
+        % linspace(freq_offset-fs/2, freq_offset+fs/2*(fft_len-2)/fft_len, fft_len);
+        Nyq = Fs/2;
+        half_res = freq_res/2;
+        if rem(N,2) % odd
+            idx = 1:(N-1)/2;
+            halfpts = (N+1)/2;
+            freq_grid(halfpts) = Nyq-half_res;
+            freq_grid(halfpts+1) = Nyq+half_res;
+        else
+            idx = 1:N/2;
+            hafpts = N/2+1;
+            freq_grid(hafpts) = Nyq;
+        end
+        freq_grid(N) = Fs-freq_res;
+        freq_grid = fftshift(freq_grid);
+        freq_grid(idx) = freq_grid(idx)-Fs;        
+    end    
+end