Comparison of exact hybrid and Langevin algorithms for QCD with Kogut-Susskind fermions

We find that the exact hybrid algorithm in simulating QCD with four flavors of Kogut-Susskind fermions at Nt=4, with mqa=0.025 in lattice units, is significantly more efficient than the exact Langevin algorithm, by at least a factor of 10. Comparing the integrated autocorrelation time for the plaquette τA and the Wilson line τWI on a 44 lattice, we find for the exact hybrid algorithm τA∼10 and τWI∼30, while for the exact Langevin algorithm τA∼150 and τWI∼300. On a 163x4 lattice, even if we were not able to collect enough statistics to measure the autocorrelation times reliably, the exact hybrid algorithm appears again to be more efficient by one order of magnitude