wolffd@0: function b = back(engine, bfuture, f, t)
wolffd@0: 
wolffd@0: if f.t ~= t
wolffd@0:   error('mixed up time stamps')
wolffd@0: end
wolffd@0: if t==1
wolffd@0:   b = back1(engine, bfuture, f, t);
wolffd@0:   return;
wolffd@0: end
wolffd@0: 
wolffd@0: bnet = bnet_from_engine(engine);
wolffd@0: ss = bnet.nnodes_per_slice;
wolffd@0: 
wolffd@0: int = engine.interface;
wolffd@0: D = engine.in_clq;
wolffd@0: C = engine.out_clq;
wolffd@0: phiD = marginalize_pot(bfuture.clpot{D}, int, engine.maximize);
wolffd@0: phiD = set_domain_pot(phiD, int+ss); % shift to slice 2
wolffd@0: phiC = marginalize_pot(f.clpot{C}, int+ss, engine.maximize);
wolffd@0: ratio = divide_by_pot(phiD, phiC);
wolffd@0: f.clpot{C} = multiply_by_pot(f.clpot{C}, ratio);
wolffd@0: 
wolffd@0: [b.clpot, seppot] = distribute_evidence(engine.jtree_engine, f.clpot, f.seppot);
wolffd@0: for c=1:length(b.clpot)
wolffd@0:   [b.clpot{c}, ll(c)] = normalize_pot(b.clpot{c});
wolffd@0: end
wolffd@0: b.t = t;