dSeparationAlgorithm.cpp

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 *       - Pierre-Henri WUILLEMIN(_at_LIP6)                                 *
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#include <agrum/base/core/list.h>
#include <agrum/BN/algorithms/dSeparationAlgorithm.h>
 
#ifdef GUM_NO_INLINE
#  include <agrum/BN/algorithms/dSeparationAlgorithm_inl.h>
#endif   // GUM_NO_INLINE
 
namespace gum {
 
  // Fill 'requisite' with the requisite nodes in dag given a query and
  // evidence.
  void dSeparationAlgorithm::requisiteNodes(const DAG&     dag,
                                            const NodeSet& query,
                                            const NodeSet& hardEvidence,
                                            const NodeSet& softEvidence,
                                            NodeSet&       requisite) const {
    // for the moment, no node is requisite
    requisite.clear();
 
    // mark the set of ancestors of the evidence
    NodeSet ev_ancestors(dag.size());
    {
      List< NodeId > anc_to_visit;
      for (const auto node: hardEvidence)
        anc_to_visit.insert(node);
      for (const auto node: softEvidence)
        anc_to_visit.insert(node);
      while (!anc_to_visit.empty()) {
        const NodeId node = anc_to_visit.front();
        anc_to_visit.popFront();
 
        if (!ev_ancestors.exists(node)) {
          ev_ancestors.insert(node);
          for (const auto par: dag.parents(node)) {
            anc_to_visit.insert(par);
          }
        }
      }
    }
 
    // create the marks indicating that we have visited a node
    NodeSet visited_from_child(dag.size());
    NodeSet visited_from_parent(dag.size());
 
    // 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
      const NodeId node      = nodes_to_visit.front().first;
      const bool   direction = nodes_to_visit.front().second;
      nodes_to_visit.popFront();
 
      // check if the node has not already been visited in the same direction
      bool already_visited;
      if (direction) {
        already_visited = visited_from_child.exists(node);
        if (!already_visited) { visited_from_child.insert(node); }
      } else {
        already_visited = visited_from_parent.exists(node);
        if (!already_visited) { visited_from_parent.insert(node); }
      }
 
      // if this is the first time we meet the node, then visit it
      if (!already_visited) {
        // mark the node as reachable if this is not a hard evidence
        const bool is_hard_evidence = hardEvidence.exists(node);
        if (!is_hard_evidence) { requisite.insert(node); }
 
        // bounce the ball toward the neighbors
        if (direction && !is_hard_evidence) {   // visit from a child
          // visit the parents
          for (const auto par: dag.parents(node)) {
            nodes_to_visit.insert(std::pair< NodeId, bool >(par, true));
          }
 
          // visit the children
          for (const auto chi: dag.children(node)) {
            nodes_to_visit.insert(std::pair< NodeId, bool >(chi, false));
          }
        } else {   // visit from a parent
          if (!hardEvidence.exists(node)) {
            // visit the children
            for (const auto chi: dag.children(node)) {
              nodes_to_visit.insert(std::pair< NodeId, bool >(chi, false));
            }
          }
          if (ev_ancestors.exists(node)) {
            // visit the parents
            for (const auto par: dag.parents(node)) {
              nodes_to_visit.insert(std::pair< NodeId, bool >(par, true));
            }
          }
        }
      }
    }
  }
 
} /* namespace gum */