get/set float_relative_precision and its documentation

3 files changed, 40 insertions, 1 deletions

diff --git a/src/python/doc/alpha_complex_user.rst b/src/python/doc/alpha_complex_user.rst
index cfd22742..b060c86e 100644
--- a/src/python/doc/alpha_complex_user.rst
+++ b/src/python/doc/alpha_complex_user.rst
@@ -27,7 +27,8 @@ Remarks
   If you pass :code:`precision = 'exact'` to :func:`~gudhi.AlphaComplex.__init__`, the filtration values are the exact
   ones converted to float. This can be very slow.
   If you pass :code:`precision = 'safe'` (the default), the filtration values are only
-  guaranteed to have a small multiplicative error compared to the exact value.
+  guaranteed to have a small multiplicative error compared to the exact value, see
+  :func:`~gudhi.AlphaComplex.set_float_relative_precision` to modify the precision.
   A drawback, when computing persistence, is that an empty exact interval [10^12,10^12] may become a
   non-empty approximate interval [10^12,10^12+10^6].
   Using :code:`precision = 'fast'` makes the computations slightly faster, and the combinatorics are still exact, but
diff --git a/src/python/gudhi/alpha_complex.pyx b/src/python/gudhi/alpha_complex.pyx
index a4888914..9af62b43 100644
--- a/src/python/gudhi/alpha_complex.pyx
+++ b/src/python/gudhi/alpha_complex.pyx
@@ -31,6 +31,10 @@ cdef extern from "Alpha_complex_interface.h" namespace "Gudhi":
         Alpha_complex_interface(vector[vector[double]] points, vector[double] weights, bool fast_version, bool exact_version) nogil except +
         vector[double] get_point(int vertex) nogil except +
         void create_simplex_tree(Simplex_tree_interface_full_featured* simplex_tree, double max_alpha_square, bool default_filtration_value) nogil except +
+        @staticmethod
+        void set_float_relative_precision(double precision) nogil
+        @staticmethod
+        double get_float_relative_precision() nogil
 
 # AlphaComplex python interface
 cdef class AlphaComplex:
@@ -133,3 +137,27 @@ cdef class AlphaComplex:
             self.this_ptr.create_simplex_tree(<Simplex_tree_interface_full_featured*>stree_int_ptr,
                                               mas, compute_filtration)
         return stree
+
+    @staticmethod
+    def set_float_relative_precision(precision):
+        """
+        :param precision: When the AlphaComplex is constructed with :code:`precision = 'safe'` (the default),
+            one can set the float relative precision of filtration values computed in
+            :func:`~gudhi.AlphaComplex.create_simplex_tree`.
+            Default is :code:`1e-5` (cf. :func:`~gudhi.AlphaComplex.get_float_relative_precision`).
+            For more details, please refer to
+            `CGAL::Lazy_exact_nt<NT>::set_relative_precision_of_to_double <https://doc.cgal.org/latest/Number_types/classCGAL_1_1Lazy__exact__nt.html>`_
+        :type precision: float
+        """
+        if precision <=0. or precision >= 1.:
+            raise ValueError("Relative precision value must be strictly greater than 0 and strictly lower than 1")
+        Alpha_complex_interface.set_float_relative_precision(precision)
+    
+    @staticmethod
+    def get_float_relative_precision():
+        """
+        :returns: The float relative precision of filtration values computation in
+            :func:`~gudhi.AlphaComplex.create_simplex_tree`.
+        :rtype: float
+        """
+        return Alpha_complex_interface.get_float_relative_precision()
diff --git a/src/python/include/Alpha_complex_interface.h b/src/python/include/Alpha_complex_interface.h
index 671af4a4..469b91ce 100644
--- a/src/python/include/Alpha_complex_interface.h
+++ b/src/python/include/Alpha_complex_interface.h
@@ -57,6 +57,16 @@ class Alpha_complex_interface {
       alpha_ptr_->create_simplex_tree(simplex_tree, max_alpha_square, default_filtration_value);
   }
 
+  static void set_float_relative_precision(double precision) {
+    // cf. Exact_alpha_complex_dD kernel type in Alpha_complex_factory.h
+    CGAL::Epeck_d<CGAL::Dynamic_dimension_tag>::FT::set_relative_precision_of_to_double(precision);
+  }
+
+  static double get_float_relative_precision() {
+    // cf. Exact_alpha_complex_dD kernel type in Alpha_complex_factory.h
+    return CGAL::Epeck_d<CGAL::Dynamic_dimension_tag>::FT::get_relative_precision_of_to_double();
+  }
+
  private:
   std::unique_ptr<Abstract_alpha_complex> alpha_ptr_;
 };