During myfun create a GUI, you cannot enter new commands in Matlab's command window. But if myfun is ready, the prompt appears again and you can start myfun again.
You can set the Tag of the created figure uniquely and reject the processing of myfun is a figure with this tag is existing already.
function myfun
TagName = 'myUniqueTag_myfun';
existing = findobj(allchild(0), 'flat', 'Tag', TagName);
if ~isempty(existing)
figure(existing(1)); % bring figure to front
return;
end
figure('Name', 'myfun', 'Tag', TagName);
...
From an earlier discussion about timer objects I've learned, that this method can fail, if myfun is called from a callback of a timer. Then several figures can be created and using figure(existing(1)) is safer than using just figure(existing).
When you are using GUIDE to create the GUI, the option "GUI allows only one instance to run (singleton)" inserts similar code.
