function z = lag(x,n,v)% PURPOSE: creates a matrix or vector of lagged values% -------------------------------------------------------% USAGE: z = lag(x,n,v)% where: x = input matrix or vector, (nobs x k)%        n = order of lag%        v = (optional) initial values (default=0)% e.g.%     z = lag(x) creates a matrix (or vector) of x, lagged 1 observations%     z = lag(x,n) creates a matrix (or vector) of x, lagged n observations%     z = lag(x,n,v) creates a matrix (or vector) of x, lagged n observations,%         with initial values taking a value v.% ------------------------------------------------------% RETURNS: z = matrix (or vector) of lags (nobs x k)% ------------------------------------------------------% NOTES: if n <= 0, z = [] is returned. While you may find this%        preverse, it is sometimes useful.%-------------------------------------------------------% SEE ALSO: mlag() %-------------------------------------------------------% written by:% James P. LeSage, Dept of Economics% University of Toledo% 2801 W. Bancroft St,% Toledo, OH 43606% jpl@jpl.econ.utoledo.eduswitch(nargin)case 1   n = 1; v = 0;   zt = ones(n,cols(x))*v;   z = [ zt; trimr(x,0,n)];case 2   v = 0;   if n < 1   z = [];   else   zt = ones(n,cols(x))*v;   z = [ zt; trimr(x,0,n)];   endcase 3   if n < 1   z = [];   else   zt = ones(n,cols(x))*v;   z = [ zt; trimr(x,0,n)];   endotherwiseerror('lag: wrong # of input arguments');end;