 will stay empty.
%
%   penm.probname = 'Example Problem 1'; penm.comment = 'comment comment';
% 
% * [optional] *userdata* will get always pass in and from any callback
%   function, can be anything. If not set, an empty array will be used
%   instead. Convenient to ease communication between the callbacks, store
%   temporary data  or data of the problem to compute with them, instead of
%   using global variables, persistent memory and similar.
%
%   penm.userdata = [];
% 
% * [optional] *opti