Deflation Methods in Fermion Inverters

I will review recent developments in matrix deflation methods, by Ronald Morgan/Walter Wilcox, Andreas Stathopoulos/Konstantinos Orginos, and Martin L\"uscher, with application to lattice QCD fermion inversion. I will begin with a short review of deflation-related work in the field. The Morgan/Wilcox algorithms using GMRES and BiCGStab for deflation will be described. Typical results for quenched (Wilson and twisted mass) and dynamical configurations (CP-PACS and ETMC) will be displayed and discussed. I will outline how inclusion of multiple right-hand sides and multiple shifts can be accommodated within versions of these methods. I will also review deflation methods based on Conjugate Gradient introduced by Stathopoulos and Orginos for hermitian systems with multiple right-hand sides as well as L\"uscher's non-hermitian domain decomposition algorithm using Generalized Conjugate Residual.}