The removal of critical slowing down
  We present promising initial results of our adaptive multigrid solver developed for application directly to the non-Hermitian Wilson-Dirac system in 4 dimensions, as opposed to the solver developed in [1] for the corresponding normal equations. The key behind the success of this algorithm is the use of an adaptive projection onto coarse grids that preserves the near null space of the system matrix. We demonstrate that the resulting algorithm has weak dependence on the gauge coupling and exhibits extremely mild critical slowing down in the chiral limit. 
M. A. Clark, J. Brannick, R. C. Brower, S. F. McCormick, T. A.   Manteuffel, J. C. Osborn, C. Rebbi