empirical analysis of some known networks. Section 5 gives
some concluding remarks.
2PRELIMINARIES
In this section, we first propose some terms and notations
about the combinatorial graph theory. These terms and
notations could play a basis role, which are necessary. Sec-
ond, we give the definition of t=k-diagnosis and t=k-diag-
nosability under the PMC model. These definitions will
welly help us to complete our goals.
2.1 Terms and Notations
In a parallel computing system, processors are connected
based on a specific interconnection network. An intercon-
nection network is conveniently represented by an undi-
rected graph. Throughout this paper, we use the terms
vertex, edge and graph to replace the terms processor, link
and network, respectively. For other fundamental graph-
theoretic and interconnection network terminologies not
defined here we follow [38].
Let G be a simple undirected graph. We use V ðGÞ and
EðGÞ to denote the sets of vertices and edges of G, respec-
tively. Here, a vertex u 2 V ðGÞ represents a processor and an
edge uv 2 E ðGÞ represents a link between vertices u and v.
Also, jV ðGÞj and jEðGÞj denote the numbers of vertices and
edges of G, respectively. For any two graphs G
1
¼
ðV ðG
1
Þ;EðG
1
ÞÞ and G
2
¼ðV ðG
2
Þ;EðG
2
ÞÞ, we denote G
1
[ G
2
(resp., G
1
\ G
2
) as a graph with vertex-set V ðG
1
Þ[ V ðG
2
Þ
(resp., V ðG
1
Þ\V ðG
2
Þ)andedge-setEðG
1
Þ[EðG
2
Þ (resp.,
EðG
1
Þ\EðG
2
Þ). For a vertex v 2 V ðGÞ, N
G
ðvÞ denotes the set
of vertices adjacent to v,calledtheneighborhood of v. The cardi-
nality of jN
G
ðvÞj is called the degree of v,denotedbyd
G
ðvÞ.If
X, Z V ðGÞ and v 2 V ðGÞ, the neighborhood of v in X is
denoted by N
X
ðvÞ :¼ N
G
ðvÞ\X,andN
X
ðZÞ :¼
S
u2Z
N
X
ðuÞ.
The subscript “G” can be removed from the notation if there is
no ambiguity. For any graph G ¼ðV ðGÞ;EðGÞÞ with one sub-
set V
0
V ðGÞ,theprivate neighbors of one vertex v 2 V
0
,
denoted by PNðvÞ, are those neighbors of v which are not
shared by other vertices in V
0
and are not themselves in V
0
,
i.e., PNðvÞ¼NðvÞðNðV
0
fvgÞ [ V
0
Þ.
The subgraph of G induced by S,denotedbyG½S,isthe
graph with the vertex-set S and the edge-set fuv j
uv 2 EðGÞ;u;v2 Sg. For any two subsets A and B of V ðGÞ,
the notation A B denotes as a set obtained by removing all
vertices in B from A. For any subset F V ,thenotation
G F denotes as a graph obtained by removing all vertices in
F from G and deleting those edges with at least one end-
vertex in F, simultaneously, i.e., V ðG FÞ¼V F , EðG
F Þ¼fuv 2 E j u; v 2 V Fg. The maximal connected sub-
graphs of G F are called components.LetmcðGÞ
denote the
number of vertices in the largest component of G. S is called a
vertex-cut of a graph G if and only if G S is disconnected or a
single-vertex. The connectivity of a graph G, denoted kðGÞ,is
defined as the minimum cardinality of a vertex cut of G.A
k-connected graph is a graph G with kðGÞk.Ak-regular
graph is maximally connected if it is k-connected.
2.2 t=k-Diagnosis under the PMC Model
We introduce some notations first. Consider a multiproces-
sor system G ¼ðV ðGÞ;EðGÞÞ. The fault-set of G is the set of
all faulty vertices of G. This paper adopts the PMC model.
Under the classical PMC model [30], any two adjacent verti-
ces are capable of performing tests on each other. For any
two adjacent vertices u; v 2 V ðGÞ, the ordered pair ðu; vÞ rep-
resents a test that the vertex u tests the vertex v. In this case, u
is called the tester and v is called the tested vertex. Thus, the
self-testing capability of G can be described by its bi-direc-
tionally oriented digraph DðGÞ¼ðV ðGÞ;AðGÞÞ. A test
assignment on G can be a sub-digraph of DðGÞ. To make the
full use of the self-diagnosing capability of G, this paper will
take DðGÞ itself as the test assignment, i.e., all nodes test all
neighboring vertices. Consider two adjacent vertices, u and
v, of a graph G. The outcome of the test conducted by u on v,
denoted by sðu; vÞ, assumes the value 0 or 1 depending on
whether u evaluates v as “fault-free” or as “faulty”, respec-
tively. We also use sðu; vÞ$
sðv; uÞ to denote the syndrome
that u and v test each other. The whole collection of the test
outcomes, denoted by s, is referred to as a syndrome on G.
The PMC model assumes that a fault-free vertex can cor-
rectly evaluate all of its neighbors, whereas the outcome of a
test conducted by a faulty vertex is completely unreliable.
The basic idea behind the t=k-diagnosis is to enhance the
self-diagnosing capability of multiprocessor at the expense
of lower diagnosis demand [15], [32], [33]. Specifically, the
t=k-diagnosable definition of a system is given as follows.
Definition 1. [33] A multiprocessor system G of n units is
t=k-diagnosable if, given any test syndrome produced by the
system under the presence of a faulty set F , all the faulty pro-
cessors can be isolated to within a set of processors F
0
, out of
which at most k processors can possibly be fault-free
ðincorrectly diagnosedÞ, jF
0
jjF jþk, provided the number
of faulty processors does not exceed t.
Next, we introduce the 0-test subgraph, say T
0
ðGÞ,ofG,
which plays a very important role in our t=k-diagnosis
algorithm.
Definition 2. [42] Given a graph G ¼ðV ðGÞ;EðGÞÞ and a syn-
drome s on G produced by a faulty set. The 0-test subgraph of
G,denotedT
0
ðGÞ, is a subgraph of G defined by V ðT
0
ðGÞÞ V
and EðT
0
ðGÞÞ ¼ fuv 2 E j sðu; vÞ¼sðv; uÞ¼0g (see Fig. 1).
3AGENERAL ALGORITHM OF t=k-DIAGNOSIS
ANALYSIS FOR SOME REGULAR NETWORKS
In this section, we will propose a general t=k-diagnosability
analysis for some regular networks to establish the t=k -diag-
nosability. First, we give some available results when the net-
work G satisfies some conditions. When a regular network G
Fig. 1. The illustration of the 0-test subgraph T
0
ðGÞ.
LIN ET AL.: THE t=k-DIAGNOSABILITY FOR REGULAR NETWORKS 3159