You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: arf.m
    path of file: ./repos/malini/Codes/FC_EC_calculation code/DynamicFC/jplv7/var_bvar
    
    the code of the file until where you have to start completion: function ylevf = arf(y,nlag,nfor,begf,transf);
% PURPOSE: estimates a autoregression of order nlag
%          and produces f-step-ahead forecasts
%-------------------------------------------------------------
% USAGE: yfor = arf(y,nlag,nfor,begf,transf)
% where:    y    = an (nobs * 1) vector in levels
%           nlag = the lag length

    
function ylevf = arf(y,nlag,nfor,begf,transf);
% PURPOSE: estimates a autoregression of order nlag
%          and produces f-step-ahead forecasts
%-------------------------------------------------------------
% USAGE: yfor = arf(y,nlag,nfor,begf,transf)
% where:    y    = an (nobs * 1) vector in levels
%           nlag = the lag length
%           nfor = the forecast horizon
%           begf = the beginning date of the forecast
%                  (defaults to length(x) + 1)
%         transf = 0, no data transformation
%                = 1, 1st differences used to estimate the model
%                = freq, seasonal differences used to estimate
%                = cal-structure growth rates used to estimate
%                  e.g., cal(1982,1,12) [see cal() function]              
%-------------------------------------------------------------
% NOTE: constant term included automatically
%-------------------------------------------------------------
% RETURNS: 
%      yfor = an nfor x 1 vector of level forecasts 
%-------------------------------------------------------------
% SEE ALSO: ar, plt_ar, prt_ar
%-------------------------------------------------------------

% written by:
% James P. LeSage, Dept of Economics
% University of Toledo
% 2801 W. Bancroft St,
% Toledo, OH 43606
% jpl@spatial-econometrics.com

if nargin == 5 % user wants us to transform the data
 if isstruct(transf) % a growth rates transform
   tform = 2;
   freq = transf.freq;
   elseif transf == 0  % no transform
   tform = 0;
   elseif transf == 1  % 1st difference transform
   tform = 1;
   elseif (transf == 1) | (transf == 4) | (transf == 12)
   tform = 3;          % seasonal differences transform
   freq = transf;
   end