% Purpose
%    opens an EPIC System file for editing.
%
% Synopsis
%    datafile = mexeps('opene',filename)
%    [dirname, datafile = mexeps('opene',filename)
%
% Description
%    It opens an EPIC System file for editing 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 or a pointer 
%    file contains a list of netCDF 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, 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.
%
% Example
%    currentfile = mexeps('opene','ctd.cdf');
%
% See Also
%    setnextr, epsclose, openr, openw
%