Complex symmetric nilpotent matrix (source code)

= Complex symmetric nilpotent matrix
{title2=$N=\begin{pmatrix}1&i\\i&-1\end{pmatrix},\quad N^2=0$}

The displayed nonzero <matrix> is symmetric under transpose but not <Hermitian>. It is <nilpotent>, so all its <eigenvalues> are zero and it cannot be <diagonalizable>. Thus real-symmetric spectral conclusions require reality or a Hermitian hypothesis; complex transpose symmetry alone is insufficient.