54 X. Xu et al. / Theoretical Computer Science 659 (2017) 53–63
processors is not greater than t. Because it is impossible that all neighbors of some processor are faulty simultaneously
in a large-scale multiprocessor system, Lai et al. [13] introduced conditional diagnosability under the assumption that all
neighbors of any processor in a multiprocessor system cannot be faulty simultaneously. Conditional diagnosability is more
realistic and appropriate than traditional diagnosability in system-level diagnosis theory. The conditional diagnosabilities
of many topologies under the PMC model or the comparison model have been studied, including folded hypercubes [32],
BC networks [33], Cayley graphs generated by transposition trees [15], shuffle-cubes [16], alternating group networks [30],
split-star graphs [17], (n, k)-star graphs [29], and arrangement graphs [18]. Recently, Hao et al. [12] have established the
general relationship between conditional diagnosability and 2-extra connectivity of symmetric graphs.
In
2012, Peng et al. [21] proposed a new measure for fault diagnosis of multiprocessor systems, namely, the g-good-
neighbor (conditional)
diagnosability, which requires that every fault-free node has at least g fault-free neighbors. The
maximum t for which the multiprocessor system G is g-good-neighbor t-diagnosable is called the g-good-neighbor di-
agnosability
of G. Peng et al. [21] established the g-good-neighbor diagnosability of the n-dimensional hypercube under the
PMC model. Meanwhile, Yuan et al. [27,28] studied the g-good-neighbor diagnosability of k-ary n-cube networks (k ≥ 3)
under the PMC model and the MM* model. Yuan et al. showed that the g-good-neighbor conditional diagnosability of 3-ary
n-cube is g(2n − g + 1)/2 − 1(resp., (g − 1)(4n − 2g + 1)/2 − 1) when g is even (resp., odd); and they determined that the
g-good-neighbor conditional diagnosability of k-ary n-cube under the PMC model and the MM* model is (2n − g + 1)2
g
− 1
for
k ≥ 4, n ≥ 3 and 0 ≤ g ≤ n. Wang et al. [24] explored 2-good-neighbor diagnosability of the Cayley graph C
n
gen-
erated
by the transposition tree
n
under the PMC model and the MM* model, and obtained that the 2-good-neighbor
diagnosability is g(n − 2) − 1, where g is the girth of C
n
(n ≥ 5).
As
a generalized version of n-dimensional star graph S
n
, the (n, k)-star graph S
n,k
, proposed by Chiang and Chen [1],
preserves most attractive properties of S
n
. Agreat deal of researches have been done already on the S
n,k
. Cheng et al.
[8] established explicit formulas for the length two path centered surface areas of (n, k )-star graph S
n,k
. Cheng et al. [5]
determined
the strong matching preclusion number for S
n,k
. Cheng et al. [6], Chang et al. [3] and Zhou [29] independently
investigated the conditional diagnosability of S
n,k
for n ≥ 4 and 2 ≤ k ≤ n − 1under the comparison diagnosis model. Chiu
et al. [9] proposed an efficient routing algorithm for S
n,k
based on the probabilistic safety vector. Yang et al. [26] explored
low order conditional connectivity of S
n,k
, and determined κ
1
(S
n,k
) = n + k − 3for n ≥ 3 and κ
2
(S
n,k
) = n + 2k − 5for n ≥ 5.
Li et al. [14] extended the conditional connectivity of S
n,k
, and obtained κ
g
(S
n,k
) = n + g(k − 2) − 1for 2 ≤ k ≤ n − 1 and
0 ≤ g ≤ n − 1.
In
this paper, we show that the g-good-neighbor diagnosability of the (n, k)-star graph S
n,k
under the PMC model
(2 ≤ k ≤ n − 1 and 1 ≤ g ≤ n − k) and the comparison model (2 ≤ k ≤ n − 1 and 2 ≤ g ≤ n − k) is n + g(k − 1) − 1,
respectively. In addition, we derive that 1-good-neighbor diagnosability of S
n,k
under the comparison model is n + k − 2for
3 ≤ k ≤ n − 1 and n ≥ 4. As a supplement, we also derive that the g-good-neighbor diagnosability of the (n, 1)-star graph
S
n,1
(1 ≤ g ≤n/2 − 1 and n ≥ 4) under the PMC model and the comparison model is n/2 − 1, respectively.
The
rest of this paper is organized as follows. Section 2 provides some preliminaries to be used in the context. Sec-
tion 3 and
Section 4 explore the g-good-neighbor diagnosability of S
n,k
under the PMC model and the comparison model,
respectively. Finally, Section 5 concludes the paper.
2. Preliminaries
2.1. Terminologies and notations
In the study of multiprocessor systems, the underlying topology is usually modeled by a graph G = (V , E), where the
vertex set V represents processors and the set of edges E represents all communication links between processors. Through-
out
this paper, we only consider an undirected graph without loops. If (u, v) is an edge in a graph G, we say that u is
adjacent to v and both of u, v are incident to the edge (u, v). Agraph H is called a subgraph of G, denoted by H ⊆ G, if
V (H) ⊆ V (G) and E(H ) ⊆ E(G). Let S be a non-empty subset of V (G). The induced subgraph by S, denoted by G[S], is a
subgraph of G whose vertex-set is S and whose edge-set is the set of those edges of G that have both end-vertices in S. The
symbol G − S denotes the induced subgraphs G[V − S]. The maximal connected subgraphs of G − S are called components.
S is called a vertex-cut of a graph G if and only if G − S is disconnected or a single-vertex set. The connectivity of a graph G,
denoted κ(G), is defined as the minimum cardinality of all vertex cuts of G. We use the notation E
G
(v) to denote the set
of edges incident with a vertex v ∈ V (G). The cardinality |E
G
(v)| is called the degree of v, denoted by deg
G
(v) (or simply
deg(v)). We denote by δ(G) the minimum degrees of vertices of G. G is d-regular if deg(v) = d for every v ∈ V (G). The
neighborhood N
G
(v) of a vertex v in G is the set of all vertices that are adjacent to v in G. The neighborhood set of S is
defined as N(S) ={u ∈ V − S | there exists some vertex v ∈ S such that (u, v) ∈ E}. Let N[S] = N(S) ∪ S. Let S be a subset
of V (G), u ∈ V (G) − S. We define N
G[S]
(u) ={v | v ∈ S, (u, v) ∈ E(G)} and deg
G[S]
(u) =|N
G[S]
(u)|. Given two sets of nodes
F
1
, F
2
⊂ V (G), the symmetric difference of two subsets F
1
and F
2
is defined as F
1
F
2
= (F
1
− F
2
) ∪ (F
2
− F
1
).
For
a given nonnegative integer g, a faulty set F of V (G) is called a g-good-neighbor faulty set, if G − F has the minimum
cardinality degree at least g. Moreover, if G − F is disconnected, the g-good-neighbor faulty set F is called g-good-neighbor
cut of G. The R
g
-connectivity of G, denoted by κ
g
(G), is the minimum cardinality over all g-good-neighbor cuts of G.