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.
               </li>
            </ul>
         </div><pre> penm.userdata = [];</pre><div>
            <ul>
               <li>[optional] <b>option settings</b> in a structure (different from defaults);   if empty or not present, defaults will be used. Can be chan