The Wolff algorithm, named after Ulli Wolff, is an algorithm for Monte Carlo simulation of the Ising model in which the unit to be flipped is not a single spin, as in the Ising model, but a cluster of them. This cluster is defined as the set of neighbouring spins sharing the same value of the spin. The Wolff algorithm is an improvement over the Swendsen–Wang algorithm because it tends to form bigger clusters.
The advantage of Wolff algorithm over other algorithms for magnetic spin simulations like single spin flip is that it allows non-local moves on the energy. One important consequence of this is that in some situations (e.g. ferromagnetic Ising model or fully frustrated Ising model), the scaling of the Multicanonic simulation is, better than, where z is the exponent associated with the critical slowing down phenomena.