Unipotent matrix
= Unipotent matrix
{title2=$(U-I)^d=0$}
A square <matrix> $U$ is unipotent when $U-I$ is nilpotent. Over an <algebraically closed field>, this is equivalent to all <eigenvalues> being one. If $j$ belongs to a <nilpotent ideal> of an operator algebra, $I+j$ is a unipotent matrix. This realizes the radical factor in the <Levi decomposition of a quiver automorphism group>.