On the preconditioned AOR iterative method for Z-matrices
  Several preconditioned AOR methods have been proposed to solve system of linear equations $Ax=b$, where $A \in \mathbb{R}^{n \times n}$ is a unit Z-matrix. The aim of this paper is to give a comparison result for a class of preconditioners $P$, where $P\in \mathbb{R}^{n\times n}$ is nonsingular, nonnegative and has unit diagonal entries. Numerical results for corresponding preconditioned GMRES methods are given to illustrate the theoretical results. 
Davod Khojasteh Salkuyeh, Mohsen Hasani and Fatemeh Panjeh Ali Beik
math.NA