The reorientation operator O also replaces a state s with a new state s O with probability P ( s → → s O | s N ) . However, this operator conserves particle number and therefore only models changes in particle velocity by redistributing particles among velocity channels. The transition probability for this operator can be determined from statistical observations (by using the maximum caliber principle) or from known single-particle dynamics (using the discretized, steady-state angular probability distribution given by the Fokker-Planck equation associated to a Langevin equation describing the reorientation dynamics), and typically takes the form P ( s → → s O | s N ) = 1 Z e − − β β H ( s N ) δ δ n ( s ) , n ( s O ) where Z is a normalization constant (also known as the partition function), H ( s N ) is an energy-like function which particles will likely minimize when changing their direction of motion, β β is a free parameter inversely proportional to the randomness of particle reorientation (analogous to the inverse temperature in thermodynamics), and δ δ n ( s ) , n ( s O ) is a Kronecker delta which ensures that particle number before n ( s ) and after reorientation n ( s O ) is unchanged.