  Hybrid Monte Carlo simulations that implement the fermion action using
multiple terms are commonly used. By the nature of their formulation they
involve multiple integration time scales in the evolution of the system through
simulation time. These different scales are usually dealt with by the
Sexton-Weingarten nested leapfrog integrator. In this scheme the choice of time
scales is somewhat restricted as each time step must be an exact multiple of
the next smallest scale in the sequence. A novel generalisation of the nested
leapfrog integrator is introduced which allows for far greater flexibility in
the choice of time scales, as each scale now must only be an exact multiple of
the smallest step size.

High Energy Physics - Lattice