  The partition function of the q-state Potts model with random ferromagnetic
couplings in the large-q limit is generally dominated by the contribution of a
single diagram of the high temperature expansion. Computing this dominant
diagram amounts to minimizing a particular submodular function. We provide a
combinatorial optimization algorithm, the optimal cooperation algorithm, which
works in polynomial time for any lattice. Practical implementation and the
speed of the method is also discussed.
