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

3 files changed, 33 insertions, 0 deletions

diff --git a/src/python/gudhi/simplex_tree.pxd b/src/python/gudhi/simplex_tree.pxd
index e748ac40..12c2065e 100644
--- a/src/python/gudhi/simplex_tree.pxd
+++ b/src/python/gudhi/simplex_tree.pxd
@@ -57,6 +57,7 @@ cdef extern from "Simplex_tree_interface.h" namespace "Gudhi":
         bool make_filtration_non_decreasing() nogil
         void compute_extended_filtration() nogil
         vector[vector[pair[int, pair[double, double]]]] compute_extended_persistence_subdiagrams(vector[pair[int, pair[double, double]]] dgm, double min_persistence) nogil
+        void reset_filtration(double filtration, int dimension) nogil
         # Iterators over Simplex tree
         pair[vector[int], double] get_simplex_and_filtration(Simplex_tree_simplex_handle f_simplex) nogil
         Simplex_tree_simplices_iterator get_simplices_iterator_begin() nogil
diff --git a/src/python/gudhi/simplex_tree.pyx b/src/python/gudhi/simplex_tree.pyx
index 20e66d9f..41b06116 100644
--- a/src/python/gudhi/simplex_tree.pyx
+++ b/src/python/gudhi/simplex_tree.pyx
@@ -358,6 +358,16 @@ cdef class SimplexTree:
         """
         return self.get_ptr().make_filtration_non_decreasing()
 
+    def reset_filtration(self, filtration, max_dim):
+        """This function resets filtration value until a given dimension.
+
+        :param filtration: New threshold value.
+        :type filtration: float.
+        :param max_dim: The maximal dimension.
+        :type max_dim: int.
+        """
+        self.get_ptr().reset_filtration(filtration, max_dim)
+
     def extend_filtration(self):
         """ Extend filtration for computing extended persistence. This function only uses the 
         filtration values at the 0-dimensional simplices, and computes the extended persistence 
diff --git a/src/python/test/test_simplex_tree.py b/src/python/test/test_simplex_tree.py
index 2137d822..1ca84c10 100755
--- a/src/python/test/test_simplex_tree.py
+++ b/src/python/test/test_simplex_tree.py
@@ -340,3 +340,25 @@ def test_simplices_iterator():
         assert st.find(simplex[0]) == True
         print("filtration is: ", simplex[1])
         assert st.filtration(simplex[0]) == simplex[1]
+
+def test_reset_filtration():
+    st = SimplexTree()
+    
+    assert st.insert([0, 1, 2], 3.) == True
+    assert st.insert([0, 3], 2.) == True
+    assert st.insert([3, 4, 5], 3.) == True
+    assert st.insert([0, 1, 6, 7], 4.) == True
+
+    for simplex in st.get_simplices():
+        assert st.filtration(simplex[0]) >= 0.
+    
+    # dimension until 5 even if simplex tree is of dimension 3 to test the limits
+    for dimension in range(0, 6):
+        st.reset_filtration(0., dimension)
+        for simplex in st.get_skeleton(3):
+            print(simplex)
+            if len(simplex[0]) > (dimension + 1):
+                assert st.filtration(simplex[0]) >= 1.
+            else:
+                assert st.filtration(simplex[0]) == 0.
+