%addOptional(PARSEOBJ, ARGNAME, DEFAULT, VALIDATOR) adds optional argument
%   ARGNAME to the input scheme of object PARSEOBJ. DEFAULT specifies the
%   value to use when the optional argument ARGNAME is not present in the
%   actual inputs to the function. The optional VALIDATOR input is the same
%   as for ADDREQUIRED.
%
%   See also inputParser, inputParser/addParameter, inputParser/addRequired, inputParser/parse 

%   Copyright 2013 The MathWorks, Inc.
%   Built-in function