On Factors of a Graph

1977 ◽  
Vol 29 (2) ◽  
pp. 438-440 ◽  
Author(s):  
Ebad Mahmoodian
Keyword(s):  
Sufficient Conditions ◽  
Common Vertex ◽  
Spanning Subgraph ◽  
F Factor ◽  
Odd Cycle ◽  
Vertex Set ◽  
Factor Theorem ◽  
Programming Techniques ◽  
Multiple Edges ◽  
Necessary And Sufficient

Let G be a graph with multiple edges. Let f be a function from the vertex set V(G) of G to the non-negative integers. An f-factor of G is a spanning subgraph F of G such that the degree (valence) of each vertex x in F is f(x). A theorem of Fulkerson, Hoffman and McAndrew [1] gives necessary and sufficient conditions to have an f-factor for a graph G with the odd-cycle property; i.e., if G has the property that either any two of its odd (simple) cycles have a common vertex, or there exists a pair of vertices, one from each cycle, which is joined by an edge. They proved this theorem using integer programming techniques, with a rather long proof. We show that this is a corollary of Tutte's f-factor theorem.

Joins of paths and cycles of equal order with sigma chromatic number 2

2021 ◽  
pp. 2250006
Author(s):  
Agnes D. Garciano ◽  
Maria Czarina T. Lagura ◽  
Reginaldo M. Marcelo
Keyword(s):  
Chromatic Number ◽  
Connected Graph ◽  
Sufficient Conditions ◽  
Necessary And Sufficient Conditions ◽  
Odd Cycle ◽  
Necessary And Sufficient ◽  
Positive Integers ◽  
Simple Connected Graph

For a simple connected graph [Formula: see text] let [Formula: see text] be a coloring of [Formula: see text] where two adjacent vertices may be assigned the same color. Let [Formula: see text] be the sum of colors of neighbors of any vertex [Formula: see text] The coloring [Formula: see text] is a sigma coloring of [Formula: see text] if for any two adjacent vertices [Formula: see text] [Formula: see text] The least number of colors required in a sigma coloring of [Formula: see text] is the sigma chromatic number of [Formula: see text] and is denoted by [Formula: see text] A sigma coloring of a graph is a neighbor-distinguishing type of coloring and it is known that the sigma chromatic number of a graph is bounded above by its chromatic number. It is also known that for a path [Formula: see text] and a cycle [Formula: see text] where [Formula: see text] [Formula: see text] and [Formula: see text] if [Formula: see text] is even. Let [Formula: see text] the join of the graphs [Formula: see text], where [Formula: see text] or [Formula: see text] [Formula: see text] and [Formula: see text] is not an odd cycle for any [Formula: see text]. It has been shown that if [Formula: see text] for [Formula: see text] and [Formula: see text] then [Formula: see text]. In this study, we give necessary and sufficient conditions under which [Formula: see text] where [Formula: see text] is the join of copies of [Formula: see text] and/or [Formula: see text] for the same value of [Formula: see text]. Let [Formula: see text] and [Formula: see text] be positive integers with [Formula: see text] and [Formula: see text] In this paper, we show that [Formula: see text] if and only if [Formula: see text] or [Formula: see text] is odd, [Formula: see text] is even and [Formula: see text]; and [Formula: see text] if and only if [Formula: see text] is even and [Formula: see text] We also obtain necessary and sufficient conditions on [Formula: see text] and [Formula: see text], so that [Formula: see text] for [Formula: see text] where [Formula: see text] or [Formula: see text] other than the cases [Formula: see text] and [Formula: see text]

scholarly journals Some sufficient conditions for graphs to have (g, f)-factors

2007 ◽  
Vol 75 (3) ◽  
pp. 447-452 ◽  
Author(s):  
Sizhong Zhou
Keyword(s):  
Sufficient Conditions ◽  
Negative Integer ◽  
Spanning Subgraph ◽  
Vertex Set

Suppose that G is a graph with vertex set V (G) and edge set E (G), and let g and f be two non-negative integer-valued functions defined on V (G) such that g (x) ≤ f (x) for each x ∈ V (G). A (g, f)-factor of G is a spanning subgraph F of G such that g (x) ≤ dF (x) ≤ f (x) for each x ∈ V (F). In this paper, some sufficient conditions for a graph to have a (g, f)-factor are given.

THE ITERATION DIGRAPHS OF GROUP RINGS OVER FINITE FIELDS

2014 ◽  
Vol 13 (05) ◽  
pp. 1350162 ◽  
Author(s):  
YANGJIANG WEI ◽  
GAOHUA TANG ◽  
JIZHU NAN
Keyword(s):  
Positive Integer ◽  
Finite Field ◽  
Finite Fields ◽  
Sufficient Conditions ◽  
Group Rings ◽  
Directed Edge ◽  
Cycle Structure ◽  
Vertex Set ◽  
Finite Commutative Ring ◽  
Necessary And Sufficient

For a finite commutative ring R and a positive integer k ≥ 2, we construct an iteration digraph G(R, k) whose vertex set is R and for which there is a directed edge from a ∈ R to b ∈ R if b = ak. In this paper, we investigate the iteration digraphs G(𝔽prCn, k) of 𝔽prCn, the group ring of a cyclic group Cn over a finite field 𝔽pr. We study the cycle structure of G(𝔽prCn, k), and explore the symmetric digraphs. Finally, we obtain necessary and sufficient conditions on 𝔽prCn and k such that G(𝔽prCn, k) is semiregular.

scholarly journals Greedoids on vertex sets of B-joins of graphs

2014 ◽  
Vol 30 (3) ◽  
pp. 335-344
Author(s):  
VADIM E. LEVIT ◽  
◽  
EUGEN MANDRESCU ◽  
Keyword(s):  
Bipartite Graph ◽  
Sufficient Conditions ◽  
Local Maximum ◽  
Stable Set ◽  
Stable Sets ◽  
The Family ◽  
Maximum Stable Set ◽  
Vertex Set ◽  
Necessary And Sufficient ◽  
Vertex Sets

Let Ψ(G) be the family of all local maximum stable sets of graph G, i.e., S ∈ Ψ(G) if S is a maximum stable set of the subgraph induced by S ∪ N(S), where N(S) is the neighborhood of S. It was shown that Ψ(G) is a greedoid for every forest G [15]. The cases of bipartite graphs, triangle-free graphs, and well-covered graphs, were analyzed in [16, 17, 18, 19, 20, 24]. If G1, G2 are two disjoint graphs, and B is a bipartite graph having E(B) as an edge set and bipartition {V (G1), V (G2)}, then by B-join of G1, G2 we mean the graph B (G1, G2) whose vertex set is V (G1) ∪ V (G2) and edge set is E(G1) ∪ E(G2) ∪ E (B). In this paper we present several necessary and sufficient conditions for Ψ(B (G1, G2)) to form a greedoid, an antimatroid, and a matroid, in terms of Ψ(G1), Ψ(G2) and E (B).

scholarly journals More on the annihilator-ideal graph of a commutative ring

2019 ◽  
Vol 18 (08) ◽  
pp. 1950160
Author(s):  
M. J. Nikmehr ◽  
S. M. Hosseini
Keyword(s):  
Commutative Ring ◽  
Sufficient Conditions ◽  
Simple Graph ◽  
Necessary And Sufficient Conditions ◽  
Star Graph ◽  
Annihilator Ideal ◽  
Vertex Set ◽  
Necessary And Sufficient

Let [Formula: see text] be a commutative ring with identity and [Formula: see text] be the set of ideals of [Formula: see text] with nonzero annihilator. The annihilator-ideal graph of [Formula: see text], denoted by [Formula: see text], is a simple graph with the vertex set [Formula: see text], and two distinct vertices [Formula: see text] and [Formula: see text] are adjacent if and only if [Formula: see text]. In this paper, we study the affinity between the annihilator-ideal graph and the annihilating-ideal graph [Formula: see text] (a well known graph with the same vertices and two distinct vertices [Formula: see text] are adjacent if and only if [Formula: see text]) associated with [Formula: see text]. All rings whose [Formula: see text] and [Formula: see text] are characterized. Among other results, we obtain necessary and sufficient conditions under which [Formula: see text] is a star graph.

scholarly journals Unicyclic Graphs Whose Completely Regular Endomorphisms form a Monoid

Mathematics ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 240
Author(s):  
Rui Gu ◽  
Hailong Hou
Keyword(s):  
Sufficient Conditions ◽  
Unicyclic Graph ◽  
Necessary And Sufficient Conditions ◽  
Unicyclic Graphs ◽  
Completely Regular ◽  
Odd Cycle ◽  
Necessary And Sufficient

In this paper, completely regular endomorphisms of unicyclic graphs are explored. Let G be a unicyclic graph and let c E n d ( G ) be the set of all completely regular endomorphisms of G. The necessary and sufficient conditions under which c E n d ( G ) forms a monoid are given. It is shown that c E n d ( G ) forms a submonoid of E n d ( G ) if and only if G is an odd cycle or G = G ( n , m ) for some odd n ≥ 3 and integer m ≥ 1 .

scholarly journals Line graph of unit graphs associated with finite commutative rings

2021 ◽  
Author(s):  
Pranjali ◽  
Amit Kumar ◽  
Pooja Sharma
Keyword(s):  
Commutative Ring ◽  
Chromatic Number ◽  
Line Graph ◽  
Sufficient Conditions ◽  
Commutative Rings ◽  
Common Vertex ◽  
Unit Graph ◽  
Vertex Set ◽  
Finite Commutative Ring ◽  
Nonzero Identity

For a given graph G, its line graph denoted by L(G) is a graph whose vertex set V (L(G)) = E(G) and {e1, e2} ∈ E(L(G)) if e1 and e2 are incident to a common vertex in G. Let R be a finite commutative ring with nonzero identity and G(R) denotes the unit graph associated with R. In this manuscript, we have studied the line graph L(G(R)) of unit graph G(R)  associated with R. In the course of the investigation, several basic properties, viz., diameter, girth, clique, and chromatic number of L(G(R)) have been determined. Further, we have derived sufficient conditions for L(G(R)) to be Planar and Hamiltonian

scholarly journals The Noncrossing Bond Poset of a Graph

10.37236/9253 ◽  
2020 ◽  
Vol 27 (4) ◽  
Author(s):  
C. Matthew Farmer ◽  
Joshua Hallam ◽  
Clifford Smyth
Keyword(s):  
Sufficient Conditions ◽  
Partition Lattice ◽  
Open Problems ◽  
Combinatorial Properties ◽  
Noncrossing Partition ◽  
Vertex Set ◽  
Connected Subgraphs ◽  
Necessary And Sufficient ◽  
Broken Circuit ◽  
Noncrossing Partition Lattice

The partition lattice and noncrossing partition lattice are well studied objects in combinatorics. Given a graph $G$ on vertex set $\{1,2,\dots, n\}$, its bond lattice, $L_G$, is the subposet of the partition lattice formed by restricting to the partitions whose blocks induce connected subgraphs of $G$. In this article, we introduce a natural noncrossing analogue of the bond lattice, the noncrossing bond poset, $NC_G$, obtained by restricting to the noncrossing partitions of $L_G$. Both the noncrossing partition lattice and the bond lattice have many nice combinatorial properties. We show that, for several families of graphs, the noncrossing bond poset also exhibits these properties. We present simple necessary and sufficient conditions on the graph to ensure the noncrossing bond poset is a lattice.  Additionally, for several families of graphs, we give combinatorial descriptions of the Möbius function and characteristic polynomial of the noncrossing bond poset. These descriptions are in terms of a noncrossing analogue of non-broken circuit (NBC) sets of the graphs and can be thought of as a noncrossing version of Whitney's NBC theorem for the chromatic polynomial. We also consider the shellability and supersolvability of the noncrossing bond poset, providing sufficient conditions for both. We end with some open problems. 

scholarly journals Restricted triangulation on circulant graphs

2018 ◽  
Vol 16 (1) ◽  
pp. 358-369 ◽  
Author(s):  
Niran Abbas Ali ◽  
Adem Kilicman ◽  
Hazim Michman Trao
Keyword(s):  
Sufficient Conditions ◽  
Necessary And Sufficient Conditions ◽  
Existence Problem ◽  
Circulant Graph ◽  
Circulant Graphs ◽  
Value Set ◽  
Vertex Set ◽  
Necessary And Sufficient

AbstractThe restricted triangulation existence problem on a given graph decides whether there exists a triangulation on the graph’s vertex set that is restricted with respect to its edge set. Let G = C(n, S) be a circulant graph on n vertices with jump value set S. We consider the restricted triangulation existence problem for G. We determine necessary and sufficient conditions on S for which G admitting a restricted triangulation. We characterize a set of jump values S(n) that has the smallest cardinality with C(n, S(n)) admits a restricted triangulation. We present the measure of non-triangulability of Kn − G for a given G.

scholarly journals On the Number of Quasi-Kernels in Digraphs

2001 ◽  
Vol 8 (7) ◽  
Author(s):  
Gregory Gutin ◽  
Khee Meng Koh ◽  
Eng Guan Tay ◽  
Anders Yeo
Keyword(s):  
Sufficient Conditions ◽  
Necessary And Sufficient Conditions ◽  
Vertex Set ◽  
Necessary And Sufficient

<p>A vertex set X of a digraph D = (V,A) is a kernel if X is independent<br /> (i.e., all pairs of distinct vertices of X are non-adjacent) and for<br />every v in V − X there exists x in X such that vx in A. A vertex set<br />X of a digraph D = (V,A) is a quasi-kernel if X is independent and<br />for every v in V − X there exist w in V − X, x in X such that either<br />vx in A or vw,wx in A: In 1994, Chvatal and Lovasz proved that every<br />digraph has a quasi-kernel. In 1996, Jacob and Meyniel proved that, <br />if  a digraph D has no kernel, then D contains at least three quasi-kernels.</p><p>We characterize digraphs with exactly one and two quasi-kernels, and,<br />thus, provide necessary and sufficient conditions for a digraph to have<br />at least three quasi-kernels. In particular, we prove that every strong<br />digraph of order at least three, which is not a 4-cycle, has at least<br />three quasi-kernels. We conjecture that every digraph with no sink<br />has a pair of disjoint quasi-kernels and provide some support to this<br />conjecture.</p>

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