Sorry that I am new to Magma.
I have a question: I can construct the group of Lie type $3E_6(C)$ and an element $a$ in it. However I cannot have Magma compute the centralizer of $a$ as it gives something like "Bad argument types". I am guessing the group is not over a finite field? Is there any way around this hindrance so Magma can compute it? Thank you!