When you ask to cancel then indx is empty, []. The empty matrix is not considered to be a scalar -- a scalar is 1 x 1 but [] is 0 x 0. And when you ask to switch on something, you need to switch on a scalar or on a character vector
You need to re-order your code. After the listdlg() test
if ~tf
osmotic_pressure= [];
disp('You have not chosen any value for ME.')
error_osm=1;
return
end
Now you can switch() indx and be certain that indx is a scalar.
