function xlag = sdiff(x,freq)% PURPOSE: generates a vector or matrix of lags% -----------------------------------------------% USAGE:    xsdiff = sdiff(x,freq)%       or: xsdiff = sdiff(x,cstruc)% Where:         x = a vector or matrix of length nobs%             freq = 4 for quarterly, =12 for monthly%           cstruc = a structure returned by cal()% -----------------------------------------------% RETURNS: xsdiff = a seasonlly differenced matrix or vector,%                   length nobs (first freq values = 0)% -----------------------------------------------% SEE ALSO: tdiff() % written by:% James P. LeSage, Dept of Economics% University of Toledo% 2801 W. Bancroft St,% Toledo, OH 43606% jpl@jpl.econ.utoledo.eduif nargin ~= 2error('Wrong # of arguments to sdiff');end;if isstruct(freq)freq = freq.freq;end;[nobs, nvar] = size(x);tmp = zeros(freq,nvar);xlag = zeros(nobs,nvar);xlag = [tmp        x(freq+1:nobs,:) - x(1:nobs-freq,:)];