Discrete Applied Mathematics 181 (2015) 33–40
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Discrete Applied Mathematics
journal homepage: www.elsevier.com/locate/dam
Fault-tolerant maximal local-connectivity on Bubble-sort
star graphs
Hongyan Cai
a
, Huiqing Liu
a,∗
, Mei Lu
b
a
Faculty of Mathematics & Computer Science, Hubei University, Wuhan 430062, China
b
Department of Mathematical Sciences, Tsinghua University, Beijing 100084, China
a r t i c l e i n f o
Article history:
Received 3 February 2014
Received in revised form 14 June 2014
Accepted 9 October 2014
Available online 4 November 2014
Keywords:
Bubble-sort star graph
Maximal local-connectivity
Fault-tolerant
a b s t r a c t
An interconnection network is usually modeled as a graph, in which vertices and
edges correspond to processor and communication links, respectively. Connectivity is an
important measurement for the fault tolerant in interconnection network. Two vertices
is maximally local-connected if the maximum number of internally vertex-disjoint paths
between them equals the minimum degree of these two vertices. In this paper, we show
that an n-dimensional Bubble-sort star graph is (2n − 5)-fault-tolerant maximally local-
connected and is also (2n − 6)-fault-tolerant one-to-many maximally local-connected.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
An interconnection network is usually modeled as an undirected graph, in which vertices and edges correspond to
processor and communication links, respectively. Let G = (V (G), E(G)) be a graph with the vertex set V (G) and edge set
E(G). For a vertex set X, N(X) is the neighbor of X , and for a subgraph H of G, let N
H
(X) = N(X ) ∩ V (H). In particular, when
X = {x}, we set N
H
(x) = N
H
({x}) and d
H
(x) = |N
H
(x)|. A singleton of G is a vertex v with d
G
(v) = 0. Let ∆(G) and δ(G) denote
the maximum and minimum degree of G, respectively. For X, Y ⊆ V (G), we denote by E
G
(X, Y ) the set of edges of G with one
end in X and other end in Y , and by e
G
(X, Y ) their number. In particular, when Y = V (G)\X, we set E
G
(X) = E
G
(X, V (G)\X ).
The distance between two vertices u and v, denoted by d
G
(u, v), is the length of the shortest path from u to v. A matching is
a set of pairwise nonadjacent edges in a graph. The induced subgraph obtained by deleting the vertices of F ⊆ V (G) from G
is denoted by G − F. We use Bondy and Murty [2] for terminology and notation not defined here.
The connectivity of a graph G, denoted by κ(G), is defined as the minimum number of vertices whose removal results in
a disconnected or trivial graph, which is a major parameter widely describing the connection status of a graph. A nontrivial
graph G is k-connected if κ(G) ≥ k. It is known that κ(G) ≤ δ(G). A graph G is maximally connected if κ(G) = δ(G). The
local-connectivity between two distinct vertices x and y is the minimum number of internally disjoint paths between x and
y. As to local-connectivity, there is a classical Menger’s Theorem (see [10]).
Theorem 1.1 (Menger’s Theorem). In any graph G with (x, y) ∈ E(G), the maximum number of pairwise internally disjoint
xy-paths is equal to the minimum number of vertices in an xy-vertex-cut.
With the continuous increasing in network size, routing in networks with faults has become unavoidable. Fault-tolerance
is especially important for interconnection network, which is directly related to the connectivity of the corresponding graph.
∗
Corresponding author.
E-mail addresses: hql_2008@163.com (H. Liu), mlu@math.tsinghua.edu.cn (M. Lu).
http://dx.doi.org/10.1016/j.dam.2014.10.006
0166-218X/© 2014 Elsevier B.V. All rights reserved.