Allow computing the signature of a split link

NathanDunfield · NathanDunfield · commit 0b1929eb8c71 · 2026-05-07T16:28:39.000-07:00
diff --git a/spherogram_src/links/invariants.py b/spherogram_src/links/invariants.py
@@ -559,6 +559,9 @@ def signature(self, new_convention=True):
           sage: L.signature(new_convention=False)
           2
         """
+        if not self.digraph().is_weakly_connected():
+            return sum([L.signature() for L in self.split_link_diagram()])
+
         m, G = self.goeritz_matrix(return_graph=True)
         correction = sum(e['sign'] for _, _, e in G.edges(sort=False)
                          if e['sign'] == e['crossing'].sign)

Original file line number	Diff line number	Diff line change
`@@ -559,6 +559,9 @@ def signature(self, new_convention=True):`
`559`	`559`	`sage: L.signature(new_convention=False)`
`560`	`560`	`2`
`561`	`561`	`"""`
	`562`	`+ if not self.digraph().is_weakly_connected():`
	`563`	`+ return sum([L.signature() for L in self.split_link_diagram()])`
	`564`	`+`
`562`	`565`	`m, G = self.goeritz_matrix(return_graph=True)`
`563`	`566`	`correction = sum(e['sign'] for _, _, e in G.edges(sort=False)`
`564`	`567`	`if e['sign'] == e['crossing'].sign)`