Filtering algorithms for two degenerate quark flavours have advanced to the point that, in 2+1 flavour simulations, the cost of the strange quark is significant compared with the light quarks. This makes efficient filtering algorithms for single flavour actions highly desirable, in particular when considering 1+1+1 flavour simulations for QED+QCD. Here we discuss two methods for filtering the RHMC algorithm that are implemented within BQCD, an open-source Fortran program for Hybrid Monte Carlo simulations.

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