text: function marginal = marginal_family(engine, i, t)
  % MARGINAL_FAMILY Compute the marginal on the specified family (jtree_unrolled_dbn)
  % marginal = marginal_family(engine, i, t)
  
  if nargin < 3, t = 1; end
  
  bnet = bnet_from_engine(engine);
  ss = length(bnet.intra);
  marginal = marginal_family(engine.sub_engine, i + (t-1)*ss);
   
  