From 5beba525795ccc2609348d5ef7c9d124af5135f5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Radek=20Hu=C5=A1ek?= <PitelVonSacek@gmail.com>
Date: Thu, 10 Dec 2015 19:44:16 +0100
Subject: [PATCH] Add optimization based on matching subgraphs
If group has size 4 and graph contains one of following
subgraphs, it cannot be group-connected:
- vertex with all neighbours of degree 2
- vertex such that 2 of 3 his neighbours has degree 2 and so
do their neighbours
- edge such that all 4 of her neighbours have degree 2
---
groupConnectivity.pyx | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)
diff --git a/groupConnectivity.pyx b/groupConnectivity.pyx
index f405d70..28c4cc8 100644
--- a/groupConnectivity.pyx
+++ b/groupConnectivity.pyx
@@ -38,9 +38,21 @@ def pathToEdges(G, path):
return ret
+def theOtherNeighbour(G, v, w):
+ """
+ Given vertex v of degree 2 returns neighbour
+ of v not equal to w.
+ """
+ N = G.neighbors(v)
+ if N[0] == w:
+ return N[1]
+ else:
+ return N[0]
+
+
def testGroupConnectivity(G, group = "Z4", getClasses = False,
useTwoCuts = True, useDoubleSubdivisions = True,
- debug = False):
+ useSubgraphs = True, debug = False):
cdef AbstractTester* tester = NULL
if group == "Z4":
tester = new Tester[Z4[int]]()
@@ -51,6 +63,20 @@ def testGroupConnectivity(G, group = "Z4", getClasses = False,
assert(tester != NULL)
+ if useSubgraphs and group in ["Z4", "Z2_2"] and not getClasses:
+ for v in G.vertex_iterator():
+ degs = sorted(G.degree(G.neighbors(v)))
+ if degs[-1] <= 2:
+ return False
+ if len(degs) == 3 and degs[0] <= 2 and degs[1] <= 2:
+ N = [ theOtherNeighbour(G, w, v) for w in G.neighbors(v) if G.degree(w) <= 2 ]
+ if G.degree(N) == [ 2, 2 ]:
+ return False
+ for (u, v, _) in G.edge_iterator():
+ if sorted(G.degree(G.neighbors(u))) == [ 2, 2, 3 ] and \
+ sorted(G.degree(G.neighbors(v))) == [ 2, 2, 3 ]:
+ return False
+
if useTwoCuts:
G.relabel()
--
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