Mohamed Barraa, Mohamed Boumazgour, A Note on the Spectrum of an Upper Triangular Operator Matrix, Proceedings of the American Mathematical Society, Vol. 131, No. 10 (Oct., 2003), pp. 3083-3088 ...

Triangular forms may be obtained constructively using sequences of elementary transformations based on elementary matrix algebra. Our main result is to define a unique canonical form for prime-power ...