I have a matrix that is given by $A e^{i q} + A^* e^{-i q}$ with $A$ a nilpotent $n\times n$ matrix. The eigenvalues I get turn out always to be independent on qof $q$ but I cannot prove it. I want to know how can I prove this (or if this alone is not sufficient for the eigenvalues to be independent on q$q$).