function theResult = at(theFile, theOffset)

% at -- Switch to the folder of a given file.
%  at('theFunction') switches to the folder of
%   'theFunction', as determined by the "which"
%   function.
%  at('theFunction', theOffset) performs as above,
%   then marches into higher directories by the
%   amount of theOffset, which must be a negative
%   integer.
 
% Copyright (C) 2000 Dr. Charles R. Denham, ZYDECO.
%  All Rights Reserved.
%   Disclosure without explicit written consent from the
%    copyright owner does not constitute publication.
 
% Version of 01-Feb-2000 22:21:09.
% Updated    22-Apr-2003 09:19:37.

if nargout > 0, theResult = []; end

if nargin < 1, help(mfilename), return, end
if nargin < 2, theOffset = 0; end
if ischar(theOffset), theOffset = eval(theOffset); end

w = which(theFile);

if isempty(w)
    w = which([theFile '/' theFile]);
    if isempty(w)
	    disp([' ## No such file: ' theFile])
	    return
    end
elseif isequal(w, 'built-in')
	disp([' ## ' theFile ' is built-in.  Try "at ' theFile '.m".'])
	return
end

[thePath, theName, theExtension, theVersion] = fileparts(w);

if any(thePath)
	cd(thePath)
	if theOffset < 0
		for i = 1:fix(abs(theOffset))
			cd ..
		end
	end
end

if nargout > 0
	theResult = pwd;
else
	disp([' ## ' pwd])
end