1 files changed, 59 insertions, 3 deletions

diff --git a/src/Simplex_tree/include/gudhi/Simplex_tree.h b/src/Simplex_tree/include/gudhi/Simplex_tree.h
index 8ab3da41..b2d380ea 100644
--- a/src/Simplex_tree/include/gudhi/Simplex_tree.h
+++ b/src/Simplex_tree/include/gudhi/Simplex_tree.h
@@ -482,7 +482,16 @@ class Simplex_tree {
   }
 
   /** \brief Returns an upper bound on the dimension of the simplicial complex. */
-  int dimension() const {
+  int upper_bound_dimension() const {
+    return dimension_;
+  }
+
+  /** \brief Returns the dimension of the simplicial complex.
+      \details This function is not constant time because it can trigger `lower_upper_bound_dimension()` if required.
+  */
+  int dimension() {
+    if (dimension_to_be_lowered_)
+      lower_upper_bound_dimension();
     return dimension_;
   }
 
@@ -591,7 +600,11 @@ class Simplex_tree {
       // if filtration value unchanged
       return std::pair<Simplex_handle, bool>(null_simplex(), false);
     }
-    // otherwise the insertion has succeeded
+    // otherwise the insertion has succeeded - size is a size_type
+    if (static_cast<int>(simplex.size()) - 1 > dimension_) {
+      // Update dimension if needed
+      dimension_ = static_cast<int>(simplex.size()) - 1;
+    }
     return res_insert;
   }
 
@@ -1254,6 +1267,9 @@ class Simplex_tree {
    * \post Some simplex tree functions require the filtration to be valid. `prune_above_filtration()`
    * function is not launching `initialize_filtration()` but returns the filtration modification information. If the
    * complex has changed , please call `initialize_filtration()` to recompute it.
+   * \post Note that the dimension of the simplicial complex may be lower after calling `prune_above_filtration()`
+   * than it was before. However, `upper_bond_dimension()` will return the old value, which remains a valid upper
+   * bound. If you care, you can call `dimension()` to recompute the exact dimension.
    */
   bool prune_above_filtration(Filtration_value filtration) {
     return rec_prune_above_filtration(root(), filtration);
@@ -1265,6 +1281,8 @@ class Simplex_tree {
     auto last = std::remove_if(list.begin(), list.end(), [=](Dit_value_t& simplex) {
         if (simplex.second.filtration() <= filt) return false;
         if (has_children(&simplex)) rec_delete(simplex.second.children());
+        // dimension may need to be lowered
+        dimension_to_be_lowered_ = true;
         return true;
       });
 
@@ -1273,6 +1291,8 @@ class Simplex_tree {
       // Removing the whole siblings, parent becomes a leaf.
       sib->oncles()->members()[sib->parent()].assign_children(sib->oncles());
       delete sib;
+      // dimension may need to be lowered
+      dimension_to_be_lowered_ = true;
       return true;
     } else {
       // Keeping some elements of siblings. Remove the others, and recurse in the remaining ones.
@@ -1284,13 +1304,46 @@ class Simplex_tree {
     return modified;
   }
 
+ private:
+  /** \brief Deep search simplex tree dimension recompute.
+   * @return True if the dimension was modified, false otherwise.
+   * \pre Be sure the simplex tree has not a too low dimension value as the deep search stops when the former dimension
+   * has been reached (cf. `upper_bound_dimension()` and `set_dimension()` methods).
+   */
+  bool lower_upper_bound_dimension() {
+    // reset automatic detection to recompute
+    dimension_to_be_lowered_ = false;
+    int new_dimension = -1;
+    // Browse the tree from the left to the right as higher dimension cells are more likely on the left part of the tree
+    for (Simplex_handle sh : complex_simplex_range()) {
+#ifdef DEBUG_TRACES
+      for (auto vertex : simplex_vertex_range(sh)) {
+        std::cout << " " << vertex;
+      }
+      std::cout << std::endl;
+#endif  // DEBUG_TRACES
+
+      int sh_dimension = dimension(sh);
+      if (sh_dimension >= dimension_)
+        // Stop browsing as soon as the dimension is reached, no need to go furter
+        return false;
+      new_dimension = std::max(new_dimension, sh_dimension);
+    }
+    dimension_ = new_dimension;
+    return true;
+  }
+
+
  public:
   /** \brief Remove a maximal simplex.
    * @param[in] sh Simplex handle on the maximal simplex to remove.
    * @return a boolean value that is an implementation detail, and that the user is supposed to ignore
    * \pre Please check the simplex has no coface before removing it.
    * \exception std::invalid_argument In debug mode, if sh has children.
-   * \post Be aware that removing is shifting data in a flat_map (initialize_filtration to be done).
+   * \post Be aware that removing is shifting data in a flat_map (`initialize_filtration()` to be done).
+   * \post Note that the dimension of the simplicial complex may be lower after calling `remove_maximal_simplex()`
+   * than it was before. However, `upper_bond_dimension()` will return the old value, which remains a valid upper
+   * bound. If you care, you can call `dimension()` to recompute the exact dimension.
    * \internal @return true if the leaf's branch has no other leaves (branch's children has been re-assigned), false otherwise.
    */
   bool remove_maximal_simplex(Simplex_handle sh) {
@@ -1309,6 +1362,8 @@ class Simplex_tree {
       // Sibling is emptied : must be deleted, and its parent must point on his own Sibling
       child->oncles()->members().at(child->parent()).assign_children(child->oncles());
       delete child;
+      // dimension may need to be lowered
+      dimension_to_be_lowered_ = true;
       return true;
     }
     return false;
@@ -1323,6 +1378,7 @@ class Simplex_tree {
   std::vector<Simplex_handle> filtration_vect_;
   /** \brief Upper bound on the dimension of the simplicial complex.*/
   int dimension_;
+  bool dimension_to_be_lowered_ = false;
 };
 
 // Print a Simplex_tree in os.