defaultTriangulation.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 Class for computing default triangulations of graphs
 *
 * @author Christophe GONZALES(@AMU) and Pierre-Henri WUILLEMIN(@LIP6)
 */
#ifndef GUM_DEFAULT_TRIANGULATION_H
#define GUM_DEFAULT_TRIANGULATION_H

#include <agrum/tools/graphs/algorithms/simplicialSet.h>
#include <agrum/tools/graphs/algorithms/triangulations/unconstrainedTriangulation.h>

namespace gum {

  /** @class DefaultTriangulation
   * @brief The default triangulation algorithm used by aGrUM
   *
   * \ingroup graph_group
   *
   * By default, this is the very class used by aGrUM for performing
   * triangulations. The algorithm used is the following:
   * # the graph passed in argument is completed by fill-ins until it becomes
   *   triangulated
   * # then an elimination tree is computed from this triangulated graph
   * # finally, a junction tree is derived from the elimination tree
   *
   * The triangulation step first tries to remove simplicial nodes, that is,
   * nodes that belong to only one clique. Then almost simplicial nodes of low
   * width are removed (almost simplicial nodes are nodes such that all but
   * one of their neighbors form a clique). Then quasi simplicial nodes are
   * removed, that is, nodes such that the ratio of the number of fill-ins to
   * add to form a clique by the number of edges in a clique is small. Then
   * nodes that create cliques of small weight are removed.
   *
   * The transformation from the elimination tree to the join tree is performed
   * bottom-up. Each time a node of the elimination tree is identified to be a
   * sub-clique, it is removed and all of its parents but one are linked to the
   * latter. The identification of sub-cliques is very fast (comparison
   * of 2 ints).
   */
  class DefaultTriangulation: public UnconstrainedTriangulation {
    public:
    // ############################################################################
    /// @name Constructors / Destructors
    // ############################################################################
    /// @{

    /// basic constructor. initialize the triangulation
    explicit DefaultTriangulation(const UndiGraph*            graph,
                                  const NodeProperty< Size >* dom_sizes,
                                  bool                        minimality   = false,
                                  double                      theRatio     = GUM_QUASI_RATIO,
                                  double                      theThreshold = GUM_WEIGHT_THRESHOLD);

    /// default constructor: initialize the triangulation for an empty graph
    explicit DefaultTriangulation(bool   minimality   = false,
                                  double theRatio     = GUM_QUASI_RATIO,
                                  double theThreshold = GUM_WEIGHT_THRESHOLD);

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

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

    /// destructor
    ~DefaultTriangulation();

    /// virtual clone constructor
    /** returns a fresh triangulation (over an empty graph) of the same
     * type as the current object
     *
     * note that we return a pointer as it enables subclasses to return
     * pointers to their types, not Triangulation pointers. See item 25 of the
     * more effective C++.*/
    virtual DefaultTriangulation* newFactory() const;

    /// virtual copy constructor
    virtual DefaultTriangulation* copyFactory() const;

    /// @}


    private:
    /// the ratio above which we consider nodes to be quasi simplicial
    double _quasi_ratio_;

    /** @brief threshold under which almost and quasi simplicial nodes can be
     * chosen to be eliminated */
    double _threshold_;


    // ############################################################################
    /// @name Operators
    // ############################################################################
    /// @{

    /// forbid copy operator
    DefaultTriangulation& operator=(const DefaultTriangulation&);

    /// @}
  };


} /* namespace gum */


#endif /* GUM_DEFAULT_TRIANGULATION_H */