) is then the reduced potential energy evaluated in state λ = λ i/k calculated using the configuration sampled in iteration n. Note that the summations run over all alchemical windows and thus information from all windows is combined to produce a free energy estimate; if only two windows are considered MBAR reduces to BAR 42 . This equation can be solved self-consistently with many solvers and these methods are implemented in the pymbar package 42 , which was used in this work to compute results with MBAR.