% Purpose
%    gets the variable value from data file.
%
% Synopsis
%    var_val = mexeps('getvar',varcode)
%    var_val = mexeps('getvar',varcode, ax_ranges)
%
% Description
%    It returns variable values from data file. The variable
%    is refered to by its variable code, varcode.  The input
%    argument ax_ranges is optional. When it is not specified, 
%    all variable values will be returned.  When it is 
%    specified, it is a 4x2 matrix with [lower upper] limits 
%    of x, y, z, and t axis of the variable you want to get. 
%
% Examples
%    Open a data file and get subset value of the first variable. 
%
%      currentfile = mexeps('openr','t5n155w.cdf');
%      varcode = 20;
%      ax_range = [[1 1];[1 1];[1 3];[1 5]];
%      temp = mexeps('getvar',varcode,ax_range);
%      % the size of temp is 15x1
%
% See Also
%    varlist, varshape, getslice
%