ok, i've found the problem, that was silly of me. i am getting a warning now, it says
"Warning: The method char/diff will be removed in a future release. Use sym/diff instead. For example diff(sym('x^2')).
After removal diff('x^2') will return diff(double('x^2')).
> In char.diff at 10
In Untitled at 34"
how can i get rid of this warning. Thanks