the update scheme of Eq. 4 is designed to constantly reducing the variance σ 2 i thereby gradually balancing the acceptance probabilities P acc (k). The c constant, along with the frequency of the scaling reset, regulates the speed of the balancing of the probabilities P acc (k). The probabilities P i acc (k) can be evaluated each few hundreds of attempted exchanges, and hence, with EAF's of the order of 20-30 ps -1 , a good balancing may be obtained in few ns or less with 1 < c < 2 and 0.001 × EAF < ω < 0.01 × EAF.