wolffd@0: function marginal = marginal_nodes(engine, nodes, t)
wolffd@0: % MARGINAL_NODES Compute the marginal on the specified query nodes (frontier)
wolffd@0: % marginal = marginal_nodes(engine, nodes, t)
wolffd@0: %
wolffd@0: % 't' specifies the time slice of the earliest node in 'nodes'.
wolffd@0: % 'nodes' cannot span more than 2 time slices.
wolffd@0: %
wolffd@0: % Example:
wolffd@0: % Consider a DBN with 2 nodes per slice.
wolffd@0: % Then t=2, nodes=[1 3] refers to node 1 in slice 2 and node 1 in slice 3,
wolffd@0: % i.e., nodes 3 and 5 in the unrolled network,
wolffd@0: 
wolffd@0: if nargin < 3, t = 1; end
wolffd@0: assert(length(nodes)==1);
wolffd@0: i = nodes(1);
wolffd@0: bigpot = engine.fwdback{i,t};
wolffd@0: bnet = bnet_from_engine(engine);
wolffd@0: ss  = length(bnet.intra);
wolffd@0: nodes = nodes + (t-1)*ss;
wolffd@0: %if t > 1, nodes = nodes + ss; end
wolffd@0: marginal = pot_to_marginal(marginalize_pot(bigpot, nodes));