wolffd@0: function bigpot = divide_by_pot(bigpot, smallpot)
wolffd@0: % DIVIDE_BY_POT bigpot /= smallpot for cpot
wolffd@0: % bigpot = divide_by_pot(bigpot, smallpot)
wolffd@0: %
wolffd@0: % smallpot's domain must be a subset of bigpot's domain.
wolffd@0: 
wolffd@0: bigpot.g = bigpot.g - smallpot.g;
wolffd@0: if sum(smallpot.sizes) > 0
wolffd@0:   mask = find_equiv_posns(smallpot.domain, bigpot.domain);
wolffd@0:   u = block(mask, bigpot.sizes);
wolffd@0:   bigpot.h(u) = bigpot.h(u) - smallpot.h;
wolffd@0:   bigpot.K(u, u) = bigpot.K(u, u) - smallpot.K;
wolffd@0: end