% Purpose
%    opens an EPIC System file for reading.
%
% Synopsis
%    datafile = mexeps('openr',filename)
%    [dirname, datafile] = mexeps('openr',filename)
%
% Description
%    It opens an EPIC System file for reading and returns the name of 
%    data file that is currently opened.  
%
%    The input argument, filename, is the EPIC System file name.  The 
%    EPIC System file can be a single netCDF data file, a single 
%    Classis EPIC data file, or a pointer file contains a list of these 
%    data files.   The output argument, datafile, is the data file name
%    without directory path.  When 2 output arguments are specified
%    both directory path name and data file name will be returned.
%    When input filename is a single netCDF data file or a single classic 
%    EPIC file, the datafile returned is the input filename; when the 
%    filename is a pointer file name, the datafile returned is the first 
%    data file listed in the pointer file.  If pointer file contains more
%    than one data files, you must use mexeps('setnextr') to open the 
%    following data files.
%
% Examples
%
%    infile = 'eps_to_plot.ptr';         
%    currentfile = mexeps('openr',infile);
%
% See Also
%    setnextr, epsclose, openw, opene
%