1. Deptartment of Mathematics, Babe? -Bolyai University, Cluj-Napoca, Romania.bodo@math.ubbcluj.ro;3. Deptartment of Mathematics, Babe? -Bolyai University, Cluj-Napoca, Romania.
Abstract:
We study matrices over general rings which are sums of nilpotent matrices. We show that over commutative rings all matrices with nilpotent trace are sums of three nilpotent matrices. We characterize 2-by-2 matrices with integer entries which are sums of two nilpotents via the solvability of a quadratic Diophantine equation. Some exemples in the case of matrices over noncommutative rings are given.