/* This file is part of libDAI - http://www.libdai.org/
*
* libDAI is licensed under the terms of the GNU General Public License version
* 2, or (at your option) any later version. libDAI is distributed without any
* warranty. See the file COPYING for more details.
*
* Copyright (C) 2006-2009 Joris Mooij [joris dot mooij at libdai dot org]
* Copyright (C) 2006-2007 Radboud University Nijmegen, The Netherlands
*/
/// \file
/// \brief Defines class JTree, which implements the junction tree algorithm
#ifndef __defined_libdai_jtree_h
#define __defined_libdai_jtree_h
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
namespace dai {
/// Exact inference algorithm using junction tree
/** The junction tree algorithm uses message passing on a junction tree to calculate
* exact marginal probability distributions ("beliefs") for specified cliques
* (outer regions) and separators (intersections of pairs of cliques).
*
* There are two variants, the sum-product algorithm (corresponding to
* finite temperature) and the max-product algorithm (corresponding to
* zero temperature).
*/
class JTree : public DAIAlgRG {
private:
/// Stores the messages
std::vector > _mes;
/// Stores the logarithm of the partition sum
Real _logZ;
public:
/// The junction tree (stored as a rooted tree)
RootedTree RTree;
/// Outer region beliefs
std::vector Qa;
/// Inner region beliefs
std::vector Qb;
/// Parameters for JTree
struct Properties {
/// Enumeration of possible JTree updates
/** There are two types of updates:
* - HUGIN similar to those in HUGIN
* - SHSH Shafer-Shenoy type
*/
DAI_ENUM(UpdateType,HUGIN,SHSH);
/// Enumeration of inference variants
/** There are two inference variants:
* - SUMPROD Sum-Product
* - MAXPROD Max-Product (equivalent to Min-Sum)
*/
DAI_ENUM(InfType,SUMPROD,MAXPROD);
/// Enumeration of elimination cost functions used for constructing the junction tree
/** The cost of eliminating a variable can be (\see [\ref KoF09], page 314)):
* - MINNEIGHBORS the number of neighbors it has in the current adjacency graph;
* - MINWEIGHT the product of the number of states of all neighbors in the current adjacency graph;
* - MINFILL the number of edges that need to be added to the adjacency graph due to the elimination;
* - WEIGHTEDMINFILL the sum of weights of the edges that need to be added to the adjacency graph
* due to the elimination, where a weight of an edge is the produt of weights of its constituent
* vertices.
* The elimination sequence is chosen greedily in order to minimize the cost.
*/
DAI_ENUM(HeuristicType,MINNEIGHBORS,MINWEIGHT,MINFILL,WEIGHTEDMINFILL);
/// Verbosity (amount of output sent to stderr)
size_t verbose;
/// Type of updates
UpdateType updates;
/// Type of inference
InfType inference;
/// Heuristic to use for constructing the junction tree
HeuristicType heuristic;
} props;
/// Name of this inference algorithm
static const char *Name;
public:
/// \name Constructors/destructors
//@{
/// Default constructor
JTree() : DAIAlgRG(), _mes(), _logZ(), RTree(), Qa(), Qb(), props() {}
/// Construct from FactorGraph \a fg and PropertySet \a opts
/** \param fg factor graph
** \param opts Parameters @see Properties
* \param automatic if \c true, construct the junction tree automatically, using the heuristic in opts['heuristic'].
*/
JTree( const FactorGraph &fg, const PropertySet &opts, bool automatic=true );
//@}
/// \name General InfAlg interface
//@{
virtual JTree* clone() const { return new JTree(*this); }
virtual std::string identify() const;
virtual Factor belief( const VarSet &vs ) const;
virtual std::vector beliefs() const;
virtual Real logZ() const;
virtual void init() {}
virtual void init( const VarSet &/*ns*/ ) {}
virtual Real run();
virtual Real maxDiff() const { return 0.0; }
virtual size_t Iterations() const { return 1UL; }
virtual void setProperties( const PropertySet &opts );
virtual PropertySet getProperties() const;
virtual std::string printProperties() const;
//@}
/// \name Additional interface specific for JTree
//@{
/// Constructs a junction tree based on the cliques \a cl (corresponding to some elimination sequence).
/** First, constructs a weighted graph, where the nodes are the elements of \a cl, and
* each edge is weighted with the cardinality of the intersection of the state spaces of the nodes.
* Then, a maximal spanning tree for this weighted graph is calculated.
* Subsequently, a corresponding region graph is built:
* - the outer regions correspond with the cliques and have counting number 1;
* - the inner regions correspond with the seperators, i.e., the intersections of two
* cliques that are neighbors in the spanning tree, and have counting number -1
* (except empty ones, which have counting number 0);
* - inner and outer regions are connected by an edge if the inner region is a
* seperator for the outer region.
* Finally, Beliefs are constructed.
* If \a verify == \c true, checks whether each factor is subsumed by a clique.
*/
void construct( const FactorGraph &fg, const std::vector &cl, bool verify=false );
/// Constructs a junction tree based on the cliques \a cl (corresponding to some elimination sequence).
/** Invokes construct() and then constructs messages.
* \see construct()
*/
void GenerateJT( const FactorGraph &fg, const std::vector &cl );
/// Returns constant reference to the message from outer region \a alpha to its \a _beta 'th neighboring inner region
const Factor & message( size_t alpha, size_t _beta ) const { return _mes[alpha][_beta]; }
/// Returns reference to the message from outer region \a alpha to its \a _beta 'th neighboring inner region
Factor & message( size_t alpha, size_t _beta ) { return _mes[alpha][_beta]; }
/// Runs junction tree algorithm using HUGIN (message-free) updates
/** \note The initial messages may be arbitrary; actually they are not used at all.
*/
void runHUGIN();
/// Runs junction tree algorithm using Shafer-Shenoy updates
/** \note The initial messages may be arbitrary.
*/
void runShaferShenoy();
/// Finds an efficient subtree for calculating the marginal of the variables in \a vs
/** First, the current junction tree is reordered such that it gets as root the clique
* that has maximal state space overlap with \a vs. Then, the minimal subtree
* (starting from the root) is identified that contains all the variables in \a vs
* and also the outer region with index \a PreviousRoot (if specified). Finally,
* the current junction tree is reordered such that this minimal subtree comes
* before the other edges, and the size of the minimal subtree is returned.
*/
size_t findEfficientTree( const VarSet& vs, RootedTree &Tree, size_t PreviousRoot=(size_t)-1 ) const;
/// Calculates the marginal of a set of variables (using cutset conditioning, if necessary)
/** \pre assumes that run() has been called already
*/
Factor calcMarginal( const VarSet& vs );
/// Calculates the joint state of all variables that has maximum probability
/** \pre Assumes that run() has been called and that \a props.inference == \c MAXPROD
*/
std::vector findMaximum() const;
//@}
};
/// Calculates upper bound to the treewidth of a FactorGraph, using the specified heuristic
/** \relates JTree
* \return a pair (number of variables in largest clique, number of states in largest clique)
*/
std::pair boundTreewidth( const FactorGraph &fg, greedyVariableElimination::eliminationCostFunction fn );
} // end of namespace dai
#endif