Boundary and its opposite vertex iterator for the simplex tree

4 files changed, 160 insertions, 1 deletions

diff --git a/src/Simplex_tree/include/gudhi/Simplex_tree.h b/src/Simplex_tree/include/gudhi/Simplex_tree.h
index d48f6616..63a7f190 100644
--- a/src/Simplex_tree/include/gudhi/Simplex_tree.h
+++ b/src/Simplex_tree/include/gudhi/Simplex_tree.h
@@ -187,6 +187,12 @@ class Simplex_tree {
   typedef Simplex_tree_boundary_simplex_iterator<Simplex_tree> Boundary_simplex_iterator;
   /** \brief Range over the simplices of the boundary of a simplex. */
   typedef boost::iterator_range<Boundary_simplex_iterator> Boundary_simplex_range;
+  /** \brief Iterator over the simplices of the boundary and its opposite vertex of a simplex.
+   *
+   * 'value_type' is std::pair<Simplex_handle, Vertex_handle>. */
+  typedef Simplex_tree_boundary_opposite_vertex_simplex_iterator<Simplex_tree> Boundary_opposite_vertex_simplex_iterator;
+  /** \brief Range over the simplices of the boundary and its opposite vertex of a simplex. */
+  typedef boost::iterator_range<Boundary_opposite_vertex_simplex_iterator> Boundary_opposite_vertex_simplex_range;
   /** \brief Iterator over the simplices of the simplicial complex.
    *
    * 'value_type' is Simplex_handle. */
@@ -296,6 +302,23 @@ class Simplex_tree {
                                   Boundary_simplex_iterator(this));
   }
 
+  /** \brief Returns a range over the simplices of the boundary and its opposite vertex of a simplex.
+   *
+   * The boundary and its opposite vertex of a simplex is the set of codimension \f$1\f$ subsimplices of the simplex.
+   * If the simplex is \f$[v_0, \cdots ,v_d]\f$, with canonical orientation induced by \f$ v_0 < \cdots < v_d \f$, the
+   * iterator enumerates the simplices of the boundary in the order:
+   * \f$[v_0,\cdots,\widehat{v_i},\cdots,v_d]\f$ for \f$i\f$ from \f$0\f$ to \f$d\f$, where \f$\widehat{v_i}\f$ means
+   * that the vertex \f$v_i\f$ is omitted from boundary, but returned as the second element of the pair, known as the
+   * the opposite vertex of the boundary.
+   *
+   * @param[in] sh Simplex for which the boundary and its opposite vertex is computed.
+   * @return Iterator on a pair of SimplexHandle (a boundary) and a VertexHandle (its opposite vertex). */
+  template<class SimplexHandle>
+  Boundary_opposite_vertex_simplex_range boundary_opposite_vertex_simplex_range(SimplexHandle sh) {
+    return Boundary_opposite_vertex_simplex_range(Boundary_opposite_vertex_simplex_iterator(this, sh),
+                                                  Boundary_opposite_vertex_simplex_iterator(this));
+  }
+
   /** @} */  // end range and iterator methods
   /** \name Constructor/Destructor
    * @{ */
diff --git a/src/Simplex_tree/include/gudhi/Simplex_tree/Simplex_tree_iterators.h b/src/Simplex_tree/include/gudhi/Simplex_tree/Simplex_tree_iterators.h
index e5522cc7..841b4d49 100644
--- a/src/Simplex_tree/include/gudhi/Simplex_tree/Simplex_tree_iterators.h
+++ b/src/Simplex_tree/include/gudhi/Simplex_tree/Simplex_tree_iterators.h
@@ -5,6 +5,7 @@
  *    Copyright (C) 2014 Inria
  *
  *    Modification(s):
+ *      - 2022/04 Vincent Rouvreau: Add Simplex_tree_boundary_opposite_vertex_simplex_iterator for alpha and cech purpose
  *      - YYYY/MM Author: Description of the modification
  */
 
@@ -17,6 +18,7 @@
 #include <boost/container/static_vector.hpp>
 
 #include <vector>
+#include <utility>  // for std::pair
 
 namespace Gudhi {
 
@@ -123,7 +125,7 @@ class Simplex_tree_boundary_simplex_iterator : public boost::iterator_facade<
 
  private:
   friend class boost::iterator_core_access;
-// valid when iterating along the SAME boundary.
+  // valid when iterating along the SAME boundary.
   bool equal(Simplex_tree_boundary_simplex_iterator const& other) const {
     return sh_ == other.sh_;
   }
@@ -178,6 +180,104 @@ class Simplex_tree_boundary_simplex_iterator : public boost::iterator_facade<
   Simplex_handle sh_;  // current Simplex_handle in the boundary
   SimplexTree * st_;  // simplex containing the simplicial complex
 };
+
+/* \brief Iterator over the simplices of the boundary and opposite vertex of a simplex.
+ *
+ * Forward iterator, value_type is std::pair<SimplexTree::Simplex_handle, SimplexTree::Vertex_handle>.*/
+template<class SimplexTree>
+class Simplex_tree_boundary_opposite_vertex_simplex_iterator : public boost::iterator_facade<
+    Simplex_tree_boundary_opposite_vertex_simplex_iterator<SimplexTree>,
+    std::pair<typename SimplexTree::Simplex_handle, typename SimplexTree::Vertex_handle> const, boost::forward_traversal_tag> {
+ public:
+  using Simplex_handle = typename SimplexTree::Simplex_handle;
+  using Vertex_handle = typename SimplexTree::Vertex_handle;
+  using Siblings = typename SimplexTree::Siblings;
+
+  // For cython purpose only. The object it initializes should be overwritten ASAP and never used before it is
+  // overwritten.
+  Simplex_tree_boundary_opposite_vertex_simplex_iterator()
+      : sib_(nullptr),
+        st_(nullptr)  {
+  }
+
+  // any end() iterator
+  explicit Simplex_tree_boundary_opposite_vertex_simplex_iterator(SimplexTree * st)
+      : last_(st->null_vertex()),
+        next_(st->null_vertex()),
+        sib_(nullptr),
+        baov_(st->null_simplex(), st->null_vertex()),
+        st_(st)  {
+  }
+
+  template<class SimplexHandle>
+  Simplex_tree_boundary_opposite_vertex_simplex_iterator(SimplexTree * st, SimplexHandle sh)
+      : last_(sh->first),
+        next_(st->null_vertex()),
+        sib_(nullptr),
+        baov_(st->null_simplex(), sh->first),
+        st_(st) {
+    // Only check once at the beginning instead of for every increment, as this is expensive.
+    if (SimplexTree::Options::contiguous_vertices)
+      GUDHI_CHECK(st_->contiguous_vertices(), "The set of vertices is not { 0, ..., n } without holes");
+    Siblings * sib = st->self_siblings(sh);
+    next_ = sib->parent();
+    sib_ = sib->oncles();
+    if (sib_ != nullptr) {
+      if (SimplexTree::Options::contiguous_vertices && sib_->oncles() == nullptr)
+        // Only relevant for edges
+        baov_.first = sib_->members_.begin()+next_;
+      else
+        baov_.first = sib_->find(next_);
+    }
+  }
+
+ private:
+  friend class boost::iterator_core_access;
+
+  // valid when iterating along the SAME boundary.
+  bool equal(Simplex_tree_boundary_opposite_vertex_simplex_iterator const& other) const {
+    return (baov_.first == other.baov_.first);
+  }
+
+  std::pair<Simplex_handle, Vertex_handle> const& dereference() const {
+   return baov_;
+  }
+
+  void increment() {
+    if (sib_ == nullptr) {
+      baov_.first = st_->null_simplex();
+      return;  // ------>>
+    }
+    Siblings * for_sib = sib_;
+    Siblings * new_sib = sib_->oncles();
+    auto rit = suffix_.rbegin();
+    for (; rit != suffix_.rend(); ++rit) {
+      baov_.first = for_sib->find(*rit);
+      for_sib = baov_.first->second.children();
+    }
+    baov_.first = for_sib->find(last_);  // baov_.first points to the right simplex now
+    suffix_.push_back(next_);
+    next_ = sib_->parent();
+    sib_ = new_sib;
+    if (suffix_.empty())
+      baov_.second = last_;
+    else
+      baov_.second = suffix_.back();
+  }
+
+  // Most of the storage should be moved to the range, iterators should be light.
+  Vertex_handle last_;  // last vertex of the simplex
+  Vertex_handle next_;  // next vertex to push in suffix_
+  // 40 seems a conservative bound on the dimension of a Simplex_tree for now,
+  // as it would not fit on the biggest hard-drive.
+  boost::container::static_vector<Vertex_handle, 40> suffix_;
+  // static_vector still has some overhead compared to a trivial hand-made
+  // version using std::aligned_storage, or compared to making suffix_ static.
+  Siblings * sib_;  // where the next search will start from
+  std::pair<Simplex_handle, Vertex_handle> baov_;  // a pair containing the current Simplex_handle in the boundary and its opposite vertex
+  SimplexTree * st_;  // simplex containing the simplicial complex
+};
+
 /*---------------------------------------------------------------------------*/
 /* \brief Iterator over the simplices of a simplicial complex.
  *
diff --git a/src/Simplex_tree/include/gudhi/Simplex_tree/Simplex_tree_siblings.h b/src/Simplex_tree/include/gudhi/Simplex_tree/Simplex_tree_siblings.h
index b53bad29..ae25d290 100644
--- a/src/Simplex_tree/include/gudhi/Simplex_tree/Simplex_tree_siblings.h
+++ b/src/Simplex_tree/include/gudhi/Simplex_tree/Simplex_tree_siblings.h
@@ -36,6 +36,7 @@ class Simplex_tree_siblings {
   template<class T> friend class Simplex_tree_boundary_simplex_iterator;
   template<class T> friend class Simplex_tree_complex_simplex_iterator;
   template<class T> friend class Simplex_tree_skeleton_simplex_iterator;
+  template<class T> friend class Simplex_tree_boundary_opposite_vertex_simplex_iterator;
 
   typedef typename SimplexTree::Vertex_handle Vertex_handle;
   typedef typename SimplexTree::Filtration_value Filtration_value;
diff --git a/src/Simplex_tree/test/simplex_tree_unit_test.cpp b/src/Simplex_tree/test/simplex_tree_unit_test.cpp
index bdd41d34..2c8a376c 100644
--- a/src/Simplex_tree/test/simplex_tree_unit_test.cpp
+++ b/src/Simplex_tree/test/simplex_tree_unit_test.cpp
@@ -991,3 +991,38 @@ BOOST_AUTO_TEST_CASE_TEMPLATE(simplex_tree_reset_filtration, typeST, list_of_tes
 
 }
 
+BOOST_AUTO_TEST_CASE_TEMPLATE(simplex_tree_boundaries_and_opposite_vertex_iterator, typeST, list_of_tested_variants) {
+  std::clog << "********************************************************************" << std::endl;
+  std::clog << "TEST OF BOUNDARIES AND OPPOSITE VERTEX ITERATORS" << std::endl;
+  typeST st;
+
+  st.insert_simplex_and_subfaces({2, 1, 0}, 3.);
+  st.insert_simplex_and_subfaces({3, 0}, 2.);
+  st.insert_simplex_and_subfaces({3, 4, 5}, 3.);
+  st.insert_simplex_and_subfaces({0, 1, 6, 7}, 4.);
+
+  /* Inserted simplex:        */
+  /*    1   6                 */
+  /*    o---o                 */
+  /*   /X\7/                  */
+  /*  o---o---o---o           */
+  /*  2   0   3\X/4           */
+  /*            o             */
+  /*            5             */
+  using Simplex = std::vector<typename typeST::Vertex_handle>;
+  // simplices must be kept sorted by vertex number for std::vector to use operator== - cf. last BOOST_CHECK
+  std::vector<Simplex> simplices = {{0, 1, 2}, {0, 3}, {0, 1, 6, 7}, {3,4,5}, {3,5}};
+  for (auto simplex : simplices) {
+    for(auto boundary_and_opposite_vertex : st.boundary_opposite_vertex_simplex_range(st.find(simplex))) {
+      Simplex output;
+      for (auto vertex : st.simplex_vertex_range(boundary_and_opposite_vertex.first)) {
+        std::clog << vertex << " ";
+        output.emplace_back(vertex);
+      }
+      std::clog << " - opposite vertex = " << boundary_and_opposite_vertex.second << std::endl;
+      output.emplace_back(boundary_and_opposite_vertex.second);
+      std::sort(output.begin(), output.end());
+      BOOST_CHECK(simplex == output);
+    }
+  }
+}