Accelerating the Hybrid Monte Carlo algorithm with ILU preconditioning

The pseudofermion action of the Hybrid Monte Carlo (HMC) algorithm for dynamical fermions is modified to directly incorporate Incomplete LU (ILU) factorisation. This reduces the stochastic noise and allows a larger molecular dynamics step-size to be taken, cutting the computational cost. Numerical tests using the two-flavour Schwinger model are presented, where a two-step ILU preconditioning of the even-odd fermion matrix allows the step-size to be increased by a factor of two over the standard even-odd formulation.