thanks for your reply
Is there a way to also look at the third order derivative?
I tried diff(utt,t), and got zero, diff(diff(diff(u,t),t),t) did not work either
But diff(diff(diff(u^2,t),t),t) did work, why is that?
Eventually I want to put a third order derivative into the equation, and I wrote a term in the weak form to represent this as utt*test(ut), but it turned out it's not doing anything..
Is there a way to also look at the third order derivative?
I tried diff(utt,t), and got zero, diff(diff(diff(u,t),t),t) did not work either
But diff(diff(diff(u^2,t),t),t) did work, why is that?
Eventually I want to put a third order derivative into the equation, and I wrote a term in the weak form to represent this as utt*test(ut), but it turned out it's not doing anything..