BayesBall.cpp

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/***************************************************************************
 *   Copyright (C) 2005 by Pierre-Henri WUILLEMIN et Christophe GONZALES   *
 *   {prenom.nom}_at_lip6.fr                                               *
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#include <agrum/BN/algorithms/BayesBall.h>

#ifdef GUM_NO_INLINE
#  include <agrum/BN/algorithms/BayesBall_inl.h>
#endif   // GUM_NO_INLINE

namespace gum {

  void BayesBall::requisiteNodes(const DAG&     dag,
                                 const NodeSet& query,
                                 const NodeSet& hardEvidence,
                                 const NodeSet& softEvidence,
                                 NodeSet&       requisite) {
    // for the moment, no node is requisite
    requisite.clear();

    // create the marks (top = first and bottom = second )
    NodeProperty< std::pair< bool, bool > > marks(dag.size());
    const std::pair< bool, bool >           empty_mark(false, false);

    // indicate that we will send the ball to all the query nodes (as children):
    // in list nodes_to_visit, the first element is the next node to send the
    // ball to and the Boolean indicates whether we shall reach it from one of
    // its children (true) or from one parent (false)
    List< std::pair< NodeId, bool > > nodes_to_visit;
    for (const auto node : query) {
      nodes_to_visit.insert(std::pair< NodeId, bool >(node, true));
    }

    // perform the bouncing ball until there is no node in the graph to send
    // the ball to
    while (!nodes_to_visit.empty()) {
      // get the next node to visit
      NodeId node = nodes_to_visit.front().first;

      // if the marks of the node do not exist, create them
      if (!marks.exists(node)) marks.insert(node, empty_mark);

      // bounce the ball toward the neighbors
      if (nodes_to_visit.front().second) {   // visit from a child
        nodes_to_visit.popFront();
        requisite.insert(node);

        if (hardEvidence.exists(node)) { continue; }

        if (!marks[node].first) {
          marks[node].first = true;   // top marked
          for (const auto par : dag.parents(node)) {
            nodes_to_visit.insert(std::pair< NodeId, bool >(par, true));
          }
        }

        if (!marks[node].second) {
          marks[node].second = true;   // bottom marked
          for (const auto chi : dag.children(node)) {
            nodes_to_visit.insert(std::pair< NodeId, bool >(chi, false));
          }
        }
      } else {   // visit from a parent
        nodes_to_visit.popFront();

        const bool is_hard_evidence = hardEvidence.exists(node);
        const bool is_evidence = is_hard_evidence || softEvidence.exists(node);

        if (is_evidence && !marks[node].first) {
          marks[node].first = true;
          requisite.insert(node);

          for (const auto par : dag.parents(node)) {
            nodes_to_visit.insert(std::pair< NodeId, bool >(par, true));
          }
        }

        if (!is_hard_evidence && !marks[node].second) {
          marks[node].second = true;

          for (const auto chi : dag.children(node)) {
            nodes_to_visit.insert(std::pair< NodeId, bool >(chi, false));
          }
        }
      }
    }
  }

} /* namespace gum */