defaultJunctionTreeStrategy.h

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/**
 *
 *   Copyright (c) 2005-2021 by Pierre-Henri WUILLEMIN(@LIP6) & Christophe GONZALES(@AMU)
 *   info_at_agrum_dot_org
 *
 *  This library is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Lesser General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this library.  If not, see <http://www.gnu.org/licenses/>.
 *
 */


/** @file
 * @brief An algorithms producing a junction given the elimination tree
 * produced by the triangulation algorithm
 *
 * @author Christophe GONZALES(@AMU) and Pierre-Henri WUILLEMIN(@LIP6)
 */

#ifndef GUM_DEFAULT_JUNCTION_TREE_STRATEGY_H
#define GUM_DEFAULT_JUNCTION_TREE_STRATEGY_H

#include <agrum/tools/graphs/algorithms/triangulations/junctionTreeStrategies/junctionTreeStrategy.h>

namespace gum {

  /** @class DefaultJunctionTreeStrategy
   * @brief An algorithm producing a junction given the elimination tree
   * produced by a triangulation algorithm
   *
   * \ingroup graph_group
   *
   */
  class DefaultJunctionTreeStrategy: public JunctionTreeStrategy {
    public:
    // ############################################################################
    /// @name Constructors / Destructors
    // ############################################################################
    /// @{

    /// default constructor
    DefaultJunctionTreeStrategy();

    /// copy constructor
    DefaultJunctionTreeStrategy(const DefaultJunctionTreeStrategy& from);

    /// move constructor
    DefaultJunctionTreeStrategy(DefaultJunctionTreeStrategy&& from);

    /// destructor
    virtual ~DefaultJunctionTreeStrategy();

    /// create a clone not assigned to any triangulation algorithm
    virtual DefaultJunctionTreeStrategy* newFactory() const final;

    /// virtual copy constructor
    /** @param triangulation if triangulation is different from nullptr, this
     * becomes the new triangulation algorithm associated with the junction tree
     * strategy */
    virtual DefaultJunctionTreeStrategy* copyFactory(StaticTriangulation* triangulation
                                                     = nullptr) const final;

    /// @}


    // ############################################################################
    /// @name Accessors / Modifiers
    // ############################################################################
    /// @{

    /** @brief indicates whether the junction tree strategy needs fill-ins
     * to work properly
     *
     * If the junctionTreeStrategy needs fill-ins to work properly, its
     * assigned triangulation instance (see method setTriangulation) will be
     * commited to compute them. */
    virtual bool requiresFillIns() const final;

    /// returns the junction tree computed
    /** The idea behind this method is that the JunctionTreeStrategy asks its
     * assigned triangulation (see method setTriangulation) all the data it
     * needs to compute correctly the junction tree. For instance, it may asks
     * for a triangulated graph or an elimination tree, or even the order of
     * elimination of the nodes, etc. All these data are available from the
     * triangulation class. Knowing these data, the junctionTreeStrategy
     * computes and returns a junction tree corresponding to the triangulated
     * graph.
     * @throws UndefinedElement is raised if no triangulation has been assigned
     * to the DefaultJunctionTreeStrategy */
    virtual const CliqueGraph& junctionTree() final;

    /// assigns the triangulation to the junction tree strategy
    /** @param the triangulation whose resulting cliques will be used to
     * construct the junction tree
     * @warning note that, by aGrUM's rule, the graph and the domain sizes
     * are not copied but only referenced by the junction tree strategy. */
    virtual void setTriangulation(StaticTriangulation* triangulation) final;

    /** @brief returns, for each node, the clique of the junction tree which was
     * created by its deletion
     * @throws UndefinedElement is raised if no triangulation has been assigned
     * to the DefaultJunctionTreeStrategy */
    virtual const NodeProperty< NodeId >& createdCliques() final;

    /** @brief returns the Id of the clique of the junction tree created by the
     * elimination of a given node during the triangulation process
     * @param id the id of the node in the original undirected graph whose
     * created clique's id is looked for
     * @throws UndefinedElement is raised if no triangulation has been assigned
     * to the DefaultJunctionTreeStrategy */
    virtual NodeId createdClique(const NodeId id) final;

    /// resets the current junction tree strategy data structures
    virtual void clear() final;

    /// @}

    private:
    /// a boolean indicating whether the junction tree has been constructed
    bool _has_junction_tree_{false};

    /// the junction tree computed by the algorithm
    CliqueGraph _junction_tree_;

    /** @brief indicates which clique of the junction tree was created
     * by the elimination of a given node (the key of the table) */
    NodeProperty< NodeId > _node_2_junction_clique_;

    /// computes a junction tree from an elimination tree
    void _computeJunctionTree_();
  };

} /* namespace gum */

#endif /* GUM_DEFAULT_JUNCTION_TREE_STRATEGY_H */