Tangential frequency filtering decompositions for unsymmetric matrices (Q1374757)

This paper is a generalization for nonsymmetric matrices of the tangential frequency filtering decomposition (TFFD) of a symmetric matrix considered by the author in Numer. Math. 78, No. 1, 119-142 (1997; reviewed above). Existence of TFFD and convergence rates of the induced iterative algorithm are presented. The convergence rates of an iterative scheme which uses a sequence of TFFDs as preconditioners are independent of the number of unknowns for a certain class of nonsymmetric matrices. Numerical experiments with linear systems arising from the discretization of convection-diffusion equations are presented.