wolffd@0: function engine = belprop_mrf2_inf_engine(mrf2, varargin) 
wolffd@0: % BELPROP_MRF2_INF_ENGINE Belief propagation for MRFs with discrete pairwise potentials
wolffd@0: % engine = belprop_mrf2_inf_engine(mrf2, ...)
wolffd@0: %
wolffd@0: % This is like belprop_inf_engine, except it is designed for mrf2, so is much faster.
wolffd@0: %
wolffd@0: % [ ... ] = belprop_mrf2_inf_engine(..., 'param1',val1, 'param2',val2, ...)
wolffd@0: % allows you to specify optional parameters as name/value pairs.
wolffd@0: % Parameters modifying behavior of enter_evidence are below [default value in brackets]
wolffd@0: %
wolffd@0: % max_iter - max. num. iterations [ 5*nnodes]
wolffd@0: % momentum - weight assigned to old message in convex combination
wolffd@0: %            (useful for damping oscillations) [0]
wolffd@0: % tol      - tolerance used to assess convergence [1e-3]
wolffd@0: % verbose - 1 means print error at every iteration [0]
wolffd@0: %
wolffd@0: % Parameters can be changed later using set_params 
wolffd@0: 
wolffd@0: 
wolffd@0: % The advantages of pairwise potentials are
wolffd@0: % (1) we can compute messages using vector-matrix multiplication
wolffd@0: % (2) we can easily specify the parameters: one potential per edge
wolffd@0: % In contrast, potentials on larger cliques are more complicated to deal with.
wolffd@0: 
wolffd@0: 
wolffd@0: nnodes = length(mrf2.adj_mat);
wolffd@0: 
wolffd@0: [engine.max_iter, engine.momentum, engine.tol, engine.verbose] = ...
wolffd@0:     process_options(varargin, 'max_iter', [], 'momentum', 0, 'tol', 1e-3, ...
wolffd@0: 		   'verbose', 0);
wolffd@0: 
wolffd@0: if isempty(engine.max_iter) % no user supplied value, so compute default
wolffd@0:   engine.max_iter = 5*nnodes;
wolffd@0:   %if acyclic(mrf2.adj_mat, 0) --- can be very slow!
wolffd@0:   %  engine.max_iter = nnodes;
wolffd@0:   %else
wolffd@0:   %  engine.max_iter = 5*nnodes;
wolffd@0:   %end
wolffd@0: end
wolffd@0: 
wolffd@0: engine.bel = cell(1, nnodes); % store results of enter_evidence here
wolffd@0: engine.mrf2 = mrf2;
wolffd@0: 
wolffd@0: engine = class(engine, 'belprop_mrf2_inf_engine');
wolffd@0: 
wolffd@0: