Merge pull request #363 from VincentRouvreau/stree_reset_filtration

A proposal for simplex_tree reset_filtration (python & C++)

2 files changed, 82 insertions, 0 deletions

diff --git a/src/Simplex_tree/include/gudhi/Simplex_tree.h b/src/Simplex_tree/include/gudhi/Simplex_tree.h
index 889dbd00..85d6c3b0 100644
--- a/src/Simplex_tree/include/gudhi/Simplex_tree.h
+++ b/src/Simplex_tree/include/gudhi/Simplex_tree.h
@@ -1667,6 +1667,37 @@ class Simplex_tree {
     return sh; // None of its faces has the same filtration.
   }
 
+ public:
+  /** \brief This function resets the filtration value of all the simplices of dimension at least min_dim. Resets all
+   * the Simplex_tree when `min_dim = 0`.
+   * `reset_filtration` may break the filtration property with `min_dim > 0`, and it is the user's responsibility to
+   * make it a valid filtration (using a large enough `filt_value`, or calling `make_filtration_non_decreasing`
+   * afterwards for instance).
+   * @param[in] filt_value The new filtration value.
+   * @param[in] min_dim The minimal dimension. Default value is 0.
+   */
+  void reset_filtration(Filtration_value filt_value, int min_dim = 0) {
+    rec_reset_filtration(&root_, filt_value, min_dim);
+    clear_filtration(); // Drop the cache.
+  }
+
+ private:
+  /** \brief Recursively resets filtration value when minimal depth <= 0.
+   * @param[in] sib Siblings to be parsed.
+   * @param[in] filt_value The new filtration value.
+   * @param[in] min_depth The minimal depth.
+   */
+  void rec_reset_filtration(Siblings * sib, Filtration_value filt_value, int min_depth) {
+    for (auto sh = sib->members().begin(); sh != sib->members().end(); ++sh) {
+      if (min_depth <= 0) {
+        sh->second.assign_filtration(filt_value);
+      }
+      if (has_children(sh)) {
+        rec_reset_filtration(sh->second.children(), filt_value, min_depth - 1);
+      }
+    }
+  }
+
  private:
   Vertex_handle null_vertex_;
   /** \brief Total number of simplices in the complex, without the empty simplex.*/
diff --git a/src/Simplex_tree/test/simplex_tree_unit_test.cpp b/src/Simplex_tree/test/simplex_tree_unit_test.cpp
index 9b5fa8fe..bdd41d34 100644
--- a/src/Simplex_tree/test/simplex_tree_unit_test.cpp
+++ b/src/Simplex_tree/test/simplex_tree_unit_test.cpp
@@ -940,3 +940,54 @@ BOOST_AUTO_TEST_CASE_TEMPLATE(generators, typeST, list_of_tested_variants) {
     BOOST_CHECK(st.edge_with_same_filtration(st.find({1,5}))==st.find({1,5}));
   }
 }
+
+BOOST_AUTO_TEST_CASE_TEMPLATE(simplex_tree_reset_filtration, typeST, list_of_tested_variants) {
+  std::clog << "********************************************************************" << std::endl;
+  std::clog << "TEST RESET FILTRATION" << 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             */
+
+  for (auto f_simplex : st.skeleton_simplex_range(3)) {
+    std::clog << "vertex = (";
+    for (auto vertex : st.simplex_vertex_range(f_simplex)) {
+      std::clog << vertex << ",";
+    }
+    std::clog << ") - filtration = " << st.filtration(f_simplex);
+    std::clog << " - dimension = " << st.dimension(f_simplex) << std::endl;
+    // Guaranteed by construction
+    BOOST_CHECK(st.filtration(f_simplex) >= 2.);
+  }
+
+  // dimension until 5 even if simplex tree is of dimension 3 to test the limits
+  for(int dimension = 5; dimension >= 0; dimension --) {
+    std::clog << "### reset_filtration - dimension = " << dimension << "\n";
+    st.reset_filtration(0., dimension);
+    for (auto f_simplex : st.skeleton_simplex_range(3)) {
+      std::clog << "vertex = (";
+      for (auto vertex : st.simplex_vertex_range(f_simplex)) {
+        std::clog << vertex << ",";
+      }
+      std::clog << ") - filtration = " << st.filtration(f_simplex);
+      std::clog << " - dimension = " << st.dimension(f_simplex) << std::endl;
+      if (st.dimension(f_simplex) < dimension)
+        BOOST_CHECK(st.filtration(f_simplex) >= 2.);
+      else
+        BOOST_CHECK(st.filtration(f_simplex) == 0.);
+    }
+  }
+
+}
+