Title: Extension of Two-level Schwarz Preconditioners to Symmetric
Indefinite Problems


Authors: Alan Leong 

Two-level overlapping Schwarz preconditioners are extended for
use for a class of large, symmetric, indefinite systems of linear
algebraic equations. The focus is on an enriched coarse space with
additional basis functions built from free space solutions of the
underlying partial differential equation. GMRES is used to
accelerate the convergence of preconditioned systems. Both additive and
hybrid Schwarz methods are considered and reports are given on
extensive numerical experiments.