Abstract:In this note a graph G is a finite 1-complex, and an imbedding of G in an orientable 2-manifold M is a geometric realization of G in M.The letter G will also be used to designate the set in M which is the realization of G. Manifolds will always be orientable 2-manifolds, and y(M) will stand for the genus of M. Given a graph G the genus y(G) of G is the smallest number y(M), for M in the collection of manifolds in which G can be imbedded.A block of G is a subgraph B of G maximal with respect to the property tha… Show more
Abstract. The commuting graph of a non-abelian group is a simple graph in which the vertices are the non-central elements of the group, and two distinct vertices are adjacent if and only if they commute. In this paper, we determine (up to isomorphism) all finite non-abelian groups whose commuting graphs are acyclic, planar or toroidal. We also derive explicit formulas for the genus of the commuting graphs of some well-known class of finite non-abelian groups, and show that, every collection of isomorphism classes of finite non-abelian groups whose commuting graphs have the same genus is finite.Mathematics Subject Classification (2010): 20D60, 05C25
Abstract. The commuting graph of a non-abelian group is a simple graph in which the vertices are the non-central elements of the group, and two distinct vertices are adjacent if and only if they commute. In this paper, we determine (up to isomorphism) all finite non-abelian groups whose commuting graphs are acyclic, planar or toroidal. We also derive explicit formulas for the genus of the commuting graphs of some well-known class of finite non-abelian groups, and show that, every collection of isomorphism classes of finite non-abelian groups whose commuting graphs have the same genus is finite.Mathematics Subject Classification (2010): 20D60, 05C25
“…In order to see this we use the result of Battle et al [2] which implies that a graph which contains m disjoint nonplanar subgraphs has genus > m . More precisely, we prove: Lemma 2.4.…”
Section: A ç V(g)ue(g) Then G-a Is the Graph Obtained From G By Delementioning
confidence: 99%
“…By the additivity theorems [2,6] they cannot all be nonplanar if G is large. Thus the omission of the planarity condition would result in only finitely many additional tilings.)…”
Section: A ç V(g)ue(g) Then G-a Is the Graph Obtained From G By Delementioning
confidence: 99%
“…Second, a large vertex-transitive graph G of a given genus cannot contain a small nonplanar graph H. For if that were the case, then G would contain many disjoint copies of H (by the vertex-transitivity). But then G would have large genus because of the additivity property of the graph genus [2], a contradiction.…”
Abstract. We describe all regular tilings of the torus and the Klein bottle. We apply this to describe, for each orientable (respectively nonorientable) surface S, all (but finitely many) vertex-transitive graphs which can be drawn on S but not on any surface of smaller genus (respectively crosscap number). In particular, we prove the conjecture of Babai that, for each g > 3 , there are only finitely many vertex-transitive graphs of genus g . In fact, they all have order < 101 g . The weaker conjecture for Cayley graphs was made by Gross and Tucker and extends Hurwitz' theorem that, for each g > 2, there are only finitely many groups that act on the surface of genus g . We also derive a nonorientable version of Hurwitz' theorem.
“…The following upper bound for g(Km V" K ) will be obtained as Proposition 1.15 in §1. E. is probably a poor upper bound, but improving on it seems to be quite difficult.…”
Section: Now Let G H and T Be Graphs Obtained By Amalgamating N Cmentioning
If
p
≤
m
p \leq m
, n then
K
m
∨
K
p
K
n
{K_m}{ \vee _{{K_p}}}{K_n}
is the graph obtained by identify ing a copy of
K
p
{K_p}
contained in
K
m
{K_m}
with a copy of
K
p
{K_p}
contained in
K
n
{K_n}
. It is shown that for all integers
p
≤
m
p \leq m
, n the genus
g
(
K
m
∨
K
p
K
n
)
g({K_m}{ \vee _{{K_p}}}{K_n})
of
K
m
∨
K
p
K
n
{K_m}{ \vee _{{K_p}}}{K_n}
is less than or equal to
g
(
K
m
)
+
g
(
K
n
)
g({K_m}) + g({K_n})
. Combining this fact with the lower bound obtained from the Euler formula, one sees that for
2
≤
p
≤
5
,
g
(
K
m
∨
K
p
K
n
)
2 \leq p \leq 5,g({K_m}{ \vee _{{K_p}}}{K_n})
is either
g
(
K
m
)
+
g
(
K
n
)
g({K_m}) + g({K_n})
or else
g
(
K
m
)
+
g
(
K
n
)
−
1
g({K_m}) + g({K_n}) - 1
. Except in a few special cases, it is determined which of these values is actually attained.
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