Perturbation semigroup of matrix algebras
  In this article we analyze the structure of the semigroup of inner perturbations in noncommutative geometry. This perturbation semigroup is associated to a unital associative *-algebra and extends the group of unitary elements of this *-algebra. We compute the perturbation semigroup for all matrix algebras. 
Niels Neumann and Walter D. van Suijlekom
math-ph math.MP