xyFourier.m
9c4736911d21TekRSA-Freq-vs-Time

xyFourier.m
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			% Perform physicist's fourier transform of the set of data points (x,y),
			% where the values of x are uniformly spaced, and return the two-sided
			% spectrum. The returned frequency vector is in linear (not angular) units,
			% freq=omega/2p*i

			function [freq_vect, sp_vect] = xyFourier(x_vect, y_vect)
			assert(length(x_vect)==length(y_vect), ...
			'lengths of x and y vectors should match')
			% We lease the check of the fact that the elements x_vect are equally
			% spaced to the user for the sake of time saving

			% Make output column if the supplied x vector is column
			iscol=iscolumn(x_vect);

			lx=x_vect(end)-x_vect(1); % Interval length
			n=length(x_vect);
			dx=lx/(n-1); % Step size

			n_os=floor(n/2); % Maximum positive frequency index

			freq_vect=1/lx*((-(n-1)+n_os):n_os);
			if iscol
			freq_vect=freq_vect(:);
			end

			sp_vect=sqrt(dx/n)*fft(y_vect(:));
			sp_vect=[sp_vect(n_os+2:end);sp_vect(1:n_os+1)];
			if ~iscol
			sp_vect=transpose(sp_vect);
			end
			end