function Px = per(x,n1,n2)%PER	Estimate the spectrum of a process using the periodogram%-----------%USAGE	Px = per(x,n1,n2) %%	The spectrum of a process x is estimated using the periodogram.%	%	x   :  input sequence%       n1  :  starting index, x(n1)%	n2  :  ending index, x(n2)%%	The periodogram is returned in Px using a linear scale.%%       If n1 and n2 are not specified the periodogram of the entire%       sequence is computed.%%  see also BART, MPER, WELCH, and SPER%%---------------------------------------------------------------% copyright 1996, by M.H. Hayes.  For use with the book % "Statistical Digital Signal Processing and Modeling"% (John Wiley & Sons, 1996).%---------------------------------------------------------------x   = x(:);if nargin == 1    n1 = 1;  n2 = length(x);  end;    Px = abs(fft(x(n1:n2),1024)).^2/(n2-n1+1);    Px(1)=Px(2);end;