This is the crucial step of the algorithm, and it is what makes the Wang and Landau algorithm non-Markovian: the stochastic process now depends on the history of the process. Hence the next time there is a proposal to a state with that particular energy E i , that proposal is now more likely refused; in this sense, the algorithm forces the system to visit all of the spectrum equally. The consequence is that the histogram H ( E ) is more and more flat. However, this flatness depends on how well-approximated the calculated entropy is to the exact entropy, which naturally depends on the value of f. To better and better approximate the exact entropy (and thus histogram's flatness), f is decreased after M proposal-acceptance steps: