some care for graphs in sage/combinat/posets/lattices.py

Author: dcoudert

src/sage/combinat/posets/lattices.py

@@ -1805,13 +1805,13 @@ def is_relatively_complemented(self, certificate=False):
                 return False
 
         for e1 in range(n - 1):
-            C = Counter(flatten([H.neighbors_out(e2) for e2 in H.neighbors_out(e1)]))
+            C = Counter(flatten([H.neighbors_out(e2) for e2 in H.neighbor_out_iterator(e1)]))
             for e3, c in C.items():
                 if c == 1 and len(H.closed_interval(e1, e3)) == 3:
                     if not certificate:
                         return False
-                    for e2 in H.neighbors_in(e3):
-                        if e2 in H.neighbors_out(e1):
+                    for e2 in H.neighbor_in_iterator(e3):
+                        if e2 in H.neighbor_out_iterator(e1):
                             break
                     return (False, (self._vertex_to_element(e1),
                                     self._vertex_to_element(e2),
@@ -1885,7 +1885,7 @@ def is_sectionally_complemented(self, certificate=False):
         n = H.order() - 1
         for e in range(2, n + 1):
             t = n
-            for lc in H.neighbors_in(e):
+            for lc in H.neighbor_in_iterator(e):
                 t = mt[t, lc]
                 if t == 0:
                     break
@@ -1988,7 +1988,7 @@ def join(L):
 
                 # Get elements more than B levels below it.
                 too_close = set(H.breadth_first_search(j,
-                                                       neighbors=H.neighbors_in,
+                                                       neighbors=H.neighbor_in_iterator,
                                                        distance=B - 2))
                 elems = [e for e in H.order_ideal([j]) if e not in too_close]
 
@@ -2378,7 +2378,7 @@ def is_atomic(self, certificate=False):
         if self.cardinality() < 3:
             return (True, None)
         H = self._hasse_diagram
-        atoms = set(H.neighbors_out(0))
+        atoms = set(H.neighbor_out_iterator(0))
         for v in H:
             if H.in_degree(v) == 1 and v not in atoms:
                 return (False, self._vertex_to_element(v))
@@ -2436,7 +2436,7 @@ def is_coatomic(self, certificate=False):
         if self.cardinality() < 3:
             return (True, None)
         H = self._hasse_diagram
-        coatoms = set(H.neighbors_in(n - 1))
+        coatoms = set(H.neighbor_in_iterator(n - 1))
         for v in H:
             if H.out_degree(v) == 1 and v not in coatoms:
                 return (False, self._vertex_to_element(v))
@@ -3782,8 +3782,8 @@ def is_dismantlable(self, certificate=False):
                     if certificate:
                         cert.append(e)
                     if i == 1 and o == 1:  # Remove inside the lattice
-                        lower = H.neighbors_in(e)[0]
-                        upper = H.neighbors_out(e)[0]
+                        lower = next(H.neighbor_in_iterator(e))
+                        upper = next(H.neighbor_out_iterator(e))
                         H.delete_vertex(e)
                         if upper not in H.depth_first_search(lower):
                             H.add_edge(lower, upper)
@@ -4125,11 +4125,11 @@ def canonical_meetands(self, e):
         H = self._hasse_diagram
         e = self._element_to_vertex(e)
         meetands = []
-        for a in H.neighbors_out(e):
-            above_a = list(H.depth_first_search(a))
+        for a in H.neighbor_out_iterator(e):
+            above_a = set(H.depth_first_search(a))
 
             def go_up(v):
-                return [v_ for v_ in H.neighbors_out(v) if v_ not in above_a]
+                return [v_ for v_ in H.neighbor_out_iterator(v) if v_ not in above_a]
 
             result = None
             for v in H.depth_first_search(e, neighbors=go_up):
@@ -4191,11 +4191,11 @@ def canonical_joinands(self, e):
         H = self._hasse_diagram
         e = self._element_to_vertex(e)
         joinands = []
-        for a in H.neighbors_in(e):
-            below_a = list(H.depth_first_search(a, neighbors=H.neighbors_in))
+        for a in H.neighbor_in_iterator(e):
+            below_a = set(H.depth_first_search(a, neighbors=H.neighbor_in_iterator))
 
             def go_down(v):
-                return [v_ for v_ in H.neighbors_in(v) if v_ not in below_a]
+                return [v_ for v_ in H.neighbor_in_iterator(v) if v_ not in below_a]
 
             result = None
             for v in H.depth_first_search(e, neighbors=go_down):