Hierarchically deflated conjugate gradient

Understand

We present a multi-level algorithm for the solution of five dimensional chiral fermion formulations, including domain wall and Mobius Fermions.

• The algorithm operates on the red-black preconditioned Hermitian operator, and directly accelerates conjugate gradients on the normal equations.
• The coarse grid representation of this matrix is next-to-next-to-next-to-nearest neighbour and multiple algorithmic advances are introduced, which help minimise the overhead of the coarse grid.
• The treatment of the coarse grids is purely four dimensional, and the bulk of the coarse grid operations are nearest neighbour.