I'm assuming you want a static method so that the first input does not have to be an object of the class. The way I could do this was to manually create a 'methods (Static)' section below my app properties. This is the same place a custom function (public or private) would appear. For example
properties (Access = private)
x
end
methods (Static)
function out = myFxn(in)
out = 2*in;
end
end
