IEEE TRANSACTIONS ON SYSTEMS, MAN, AND CYBERNETICS—PART A: SYSTEMS AND HUMANS, VOL. 39, NO. 6, NOVEMBER 2009 1247
A Simple Universal Generating Function Method to
Search for All Minimal Paths in Networks
Wei-Chang Yeh, Senior Member, IEEE
Abstract—Evaluating network reliability is an important
topic in planning, designing, and control of systems, and the
minimal-path (MP) set is one of the fundamental tools for evaluat-
ing network reliability. A straightforward and simple algorithm is
presented here for finding all MPs before calculating the binary-
state network reliability between the source node and the sink
node (i.e., one-to-one reliability). It is based on the universal
generating function method (UGFM) and a generalized compo-
sition operator. The computational complexity of the proposed
algorithm is also analyzed. Finally, an example is given to illustrate
how all MPs are generated using the proposed UGFM.
Index Terms—Binary-state, minimal path (MP), network
reliability, universal generating function method (UGFM).
ACRONYM
1
MP/MC Minimal path/cut.
UGF Universal generating function.
UGFM UGF method.
N
OTATION
|•| The number of elements of •, e.g., |V | is the
number of nodes in V .
Pr(•) Probability of •.
G(V,E) Connected network with the node set V =
{1, 2,...,n} and the edge set E, where 1 and n
are the specified source node and the sink node,
respectively. For example, Fig. 1 is a network.
m Number of edges in the graph.
e
ij
e
ij
∈ E is a directed edge from nodes i to j.
ε
i
1
,i
2
,...,i
k
Edge subset {e
i
1
i
2
,e
i
2
i
3
,...,e
i
k−1
i
k
}, e.g.,
ε
1235
= {e
12
,e
23
,e
35
}.
u(i) Node UGF of node i (see the details in
Section II).
U(i) Subnet UGF of node i (see the details in
Section II). Note that U(1) = u(1).
Manuscript received June 29, 2007; revised June 3, 2008 and
September 23, 2008. First published September 4, 2009; current version
published October 16, 2009. This work was supported in part by the National
Science Council of Taiwan under Grant NSC 95-2221-E-007-180-MY2. This
paper was recommended by Associate Editor L. Fang.
The author is with the Department of Industrial Engineering and Engineering
Management, National Tsing Hua University, Hsinchu 300, Taiwan (e-mail:
yeh@ieee.org).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TSMCA.2009.2026209
1
The singular and plural of an acronym are always spelled the same.
Fig. 1. Sample network.
⊗ Composition operator for UGFMs (see the details
in Section II).
⊕ Special operator for the proposed UGFMs, e.g.,
A ⊕ B ⊕ C = {A, B, C}.
∈, /∈ If B ∈ ( /∈)•, then B is (not) a term in •, where •
is a node UGF or a subnet UGF. For example, ε
10
,
ε
12
, and ε
14
∈ u(1) if u(1) = ε
10
⊕ ε
12
⊕ ε
14
.
V
[i]
V
[i]
= {j ∈ V |e
ij
∈ E for all j}.
[i] ith node added in some subnet UGF.
N
OMENCLATURE
Reliability Probability that there is at least a
path of working edges between two
given nodes.
MP/MC It is a path/cut set such that if any
arc is removed from this path/cut
set, then the remaining set is no
longer a path/cut set. For example,
{e
12
,e
24
,e
43
,e
35
,e
56
} is an MC
between nodes 1 and 6 in Fig. 1 if
e
12
, e
24
, e
43
, e
35
, and e
56
are undi-
rected. The MP/MC search is tied
to the graph-theory concepts and
connectivity measures. Probabilis-
tic techniques usually associate the
connectivity level of a network
with the availability and/or reliabil-
ity of the communication paths be-
tween specific network node pairs.
MP candidates Subsets of any MP.
Node UGF UGF for the basic element of
UGFMs.
Subnet UGF Grouped UGF formed by node
UGFs.
Composition operator Operator is used to unify node
UGFs to subnet UGFs.
State Node v is a state with respect to
node u if e
uv
∈ E, e.g., nodes 2
and 4 are all states of node 1
in Fig. 1.
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