function engine = hmm_inf_engine(bnet, varargin)% HMM_INF_ENGINE Inference engine for DBNs which uses the forwards-backwards algorithm.% engine = hmm_inf_engine(bnet, ...)%% The following optional arguments can be specified in the form of name/value pairs:% [default value in brackets]%% maximize - 1 means max-product, 0 means sum-product [0]%% The DBN is converted to an HMM with a single meganode, but the observed nodes remain factored.% This can be faster than jtree if the num. hidden nodes is low, because of lower constant factors.%% All hidden nodes must be discrete.% All observed nodes are assumed to be leaves, i.e., they cannot be parents of anything.% The parents of each observed leaf are assumed to be a subset of the hidden nodes within the same slice.% The only exception is if bnet is an AR-HMM, where the parents are assumed to be self in the% previous slice (continuous), plus all the discrete nodes in the current slice.ss = bnet.nnodes_per_slice;engine.maximize = 0;% parse optional paramsargs = varargin;nargs = length(args);if nargs > 0  for i=1:2:nargs    switch args{i},     case 'maximize', engine.maximize = args{i+1};     otherwise,        error(['invalid argument name ' args{i}]);           end  endend% Stuff to do with speeding up marginal_family[int, engine.persist, engine.transient] = compute_interface_nodes(bnet.intra, bnet.inter);engine.persist_bitv = zeros(1, ss);engine.persist_bitv(engine.persist) = 1;ns = bnet.node_sizes(:);ns(bnet.observed) = 1;ns(bnet.observed+ss) = 1;engine.eff_node_sizes = ns;for o=bnet.observed(:)'  %if bnet.equiv_class(o,1) ~= bnet.equiv_class(o,2)  %  error(['observed node ' num2str(o) ' is not tied'])  %end  cs = children(bnet.dag, o);  if ~isempty(cs)    error(['observed node ' num2str(o) ' is not allowed children'])  endend[engine.startprob, engine.transprob, engine.obsprob] = dbn_to_hmm(bnet);% This is where we will store the results between enter_evidence and marginal_nodesengine.one_slice_marginal = [];engine.two_slice_marginal = [];ss = length(bnet.intra);engine.evidence = [];engine.node_sizes = [];% avoid the need to do bnet_from_engine, which is slowengine.slice_size = ss;engine.parents = bnet.parents;engine = class(engine, 'hmm_inf_engine', inf_engine(bnet));