scholarly journals Pfaffian Orientation and Enumeration of Perfect Matchings for some Cartesian Products of Graphs

10.37236/141 ◽  
2009 ◽  
Vol 16 (1) ◽  
Author(s):  
Feng-Gen Lin ◽  
Lian-Zhu Zhang
Keyword(s):  
Cartesian Product ◽  
Perfect Matchings ◽  
Upper And Lower Bounds ◽  
Cartesian Products ◽  
Pfaffian Orientation ◽  
Enumeration Problem ◽  
General Graphs ◽  
Skew Adjacency Matrix ◽  
Product Of Graphs ◽  
Equivalent Conditions

The importance of Pfaffian orientations stems from the fact that if a graph $G$ is Pfaffian, then the number of perfect matchings of $G$ (as well as other related problems) can be computed in polynomial time. Although there are many equivalent conditions for the existence of a Pfaffian orientation of a graph, this property is not well-characterized. The problem is that no polynomial algorithm is known for checking whether or not a given orientation of a graph is Pfaffian. Similarly, we do not know whether this property of an undirected graph that it has a Pfaffian orientation is in NP. It is well known that the enumeration problem of perfect matchings for general graphs is NP-hard. L. Lovász pointed out that it makes sense not only to seek good upper and lower bounds of the number of perfect matchings for general graphs, but also to seek special classes for which the problem can be solved exactly. For a simple graph $G$ and a cycle $C_n$ with $n$ vertices (or a path $P_n$ with $n$ vertices), we define $C_n$ (or $P_n)\times G$ as the Cartesian product of graphs $C_n$ (or $P_n$) and $G$. In the present paper, we construct Pfaffian orientations of graphs $C_4\times G$, $P_4\times G$ and $P_3\times G$, where $G$ is a non bipartite graph with a unique cycle, and obtain the explicit formulas in terms of eigenvalues of the skew adjacency matrix of $\overrightarrow{G}$ to enumerate their perfect matchings by Pfaffian approach, where $\overrightarrow{G}$ is an arbitrary orientation of $G$.

scholarly journals A NOTE ON EDGE-CONNECTIVITY OF THE CARTESIAN PRODUCT OF GRAPHS

2011 ◽  
Vol 84 (1) ◽  
pp. 171-176
Author(s):  
LAKOA FITINA ◽  
C. T. LENARD ◽  
T. M. MILLS
Keyword(s):  
Cartesian Product ◽  
Edge Connectivity ◽  
Cartesian Products ◽  
Cartesian Product Of Graphs ◽  
Necessary And Sufficient ◽  
Product Of Graphs ◽  
Cartesian Products Of Graphs

AbstractThe main aim of this paper is to establish conditions that are necessary and sufficient for the edge-connectivity of the Cartesian product of two graphs to equal the sum of the edge-connectivities of the factors. The paper also clarifies an issue that has arisen in the literature on Cartesian products of graphs.

scholarly journals The G-Convexity and the G-Centroids of Composite Graphs

Mathematics ◽  
2020 ◽  
Vol 8 (11) ◽  
pp. 1927
Author(s):  
Prakash Veeraraghavan
Keyword(s):  
Cartesian Product ◽  
Facility Location Problem ◽  
Academic Community ◽  
Approximate Algorithm ◽  
Arbitrary Graph ◽  
Cartesian Products ◽  
Composite Graph ◽  
As Graph ◽  
The Relationship ◽  
General Graphs

The graph centroids defined through a topological property of a graph called g-convexity found its application in various fields. They have classified under the “facility location” problem. However, the g-centroid location for an arbitrary graph is NP-hard. Thus, it is necessary to devise an approximation algorithm for general graphs and polynomial-time algorithms for some special classes of graphs. In this paper, we study the relationship between the g-centroids of composite graphs and their factors under various well-known graph operations such as graph Joins, Cartesian products, Prism, and the Corona. For the join of two graphs G1 and G2, the weight sequence of the composite graph does not depend on the weight sequences of its factors; rather it depends on the incident pattern of the maximum cliques of G1 and G2. We also characterize the structure of the g-centroid under various cases. For the Cartesian product of G1 and G2 and the prism of a graph, we establish the relationship between the g-centroid of a composite graph and its factors. Our results will facilitate the academic community to focus on the factor graphs while designing an approximate algorithm for a composite graph.

Optimal Diffusion Schemes and Load Balancing on Product Graphs

2004 ◽  
Vol 14 (01) ◽  
pp. 61-73 ◽  
Author(s):  
ROBERT ELSÄSSER ◽  
BURKHARD MONIEN ◽  
ROBERT PREIS ◽  
ANDREAS FROMMER
Keyword(s):  
Load Balancing ◽  
Nearest Neighbor ◽  
Cartesian Product ◽  
Cartesian Products ◽  
Optimal Scheme ◽  
Alternating Direction ◽  
Product Graphs ◽  
Diffusion Scheme ◽  
General Graphs ◽  
Number Of Iterations

We discuss nearest neighbor load balancing schemes on processor networks which are represented by a cartesian product of graphs and present a new optimal diffusion scheme for general graphs. In the first part of the paper, we introduce the Alternating-Direction load balancing scheme, which reduces the number of load balance iterations by a factor of 2 for cartesian products of graphs. The resulting flow is theoretically analyzed and can be very high for certain cases. Therefore, we further present the Mixed-Direction scheme which needs the same number of iterations but computes in most cases a much smaller flow. In the second part of the paper, we present a simple optimal diffusion scheme for general graphs, calculating a balancing flow which is minimal in the l2 norm. It is based on the spectra of the graph representing the network and needs only m-1 iterations to balance the load with m being the number of distinct eigenvalues. Known optimal diffusion schemes have the same performance, however the optimal scheme presented in this paper can be implemented in a very simple manner. The number of iterations of optimal diffusion schemes is independent of the load scenario and, thus, they are practical for networks which represent graphs with known spectra. Finally, our experiments exhibit that the new optimal scheme can successfully be combined with the Alternating-Direction and Mixed-Direction schemes for efficient load balancing on product graphs.

scholarly journals Game Chromatic Number of Cartesian Product Graphs

10.37236/796 ◽  
2008 ◽  
Vol 15 (1) ◽  
Author(s):  
T. Bartnicki ◽  
B. Brešar ◽  
J. Grytczuk ◽  
M. Kovše ◽  
Z. Miechowicz ◽  
...  
Keyword(s):  
Chromatic Number ◽  
Cartesian Product ◽  
Chromatic Numbers ◽  
Cartesian Products ◽  
Game Chromatic Number ◽  
Coloring Number ◽  
Product Graphs ◽  
Complete Bipartite Graphs ◽  
Game Coloring Number ◽  
Product Of Graphs

The game chromatic number $\chi _{g}$ is considered for the Cartesian product $G\,\square \,H$ of two graphs $G$ and $H$. Exact values of $\chi _{g}(K_2\square H)$ are determined when $H$ is a path, a cycle, or a complete graph. By using a newly introduced "game of combinations" we show that the game chromatic number is not bounded in the class of Cartesian products of two complete bipartite graphs. This result implies that the game chromatic number $\chi_{g}(G\square H)$ is not bounded from above by a function of game chromatic numbers of graphs $G$ and $H$. An analogous result is derived for the game coloring number of the Cartesian product of graphs.

scholarly journals Strong geodetic problem on Cartesian products of graphs

2018 ◽  
Vol 52 (1) ◽  
pp. 205-216 ◽  
Author(s):  
Vesna Iršič ◽  
Sandi Klavžar
Keyword(s):  
Shortest Path ◽  
Upper Bound ◽  
Cartesian Product ◽  
Cartesian Products ◽  
Cartesian Product Of Graphs ◽  
Geodetic Number ◽  
Recent Variation ◽  
Product Of Graphs ◽  
Strong Geodetic Number ◽  
Cartesian Products Of Graphs

The strong geodetic problem is a recent variation of the geodetic problem. For a graph G, its strong geodetic number sg(G) is the cardinality of a smallest vertex subset S, such that each vertex of G lies on a fixed shortest path between a pair of vertices from S. In this paper, the strong geodetic problem is studied on the Cartesian product of graphs. A general upper bound for sg(G □ H) is determined, as well as exact values for Km □ Kn, K1,k □ Pl, and prisms over Kn–e. Connections between the strong geodetic number of a graph and its subgraphs are also discussed.

scholarly journals Peg Solitaire on Cartesian Products of Graphs

2021 ◽  
Vol 37 (3) ◽  
pp. 907-917
Author(s):  
Martin Kreh ◽  
Jan-Hendrik de Wiljes
Keyword(s):  
Cartesian Product ◽  
Cartesian Products ◽  
Connected Graphs ◽  
Grid Graphs ◽  
Cartesian Products Of Graphs

AbstractIn 2011, Beeler and Hoilman generalized the game of peg solitaire to arbitrary connected graphs. In the same article, the authors proved some results on the solvability of Cartesian products, given solvable or distance 2-solvable graphs. We extend these results to Cartesian products of certain unsolvable graphs. In particular, we prove that ladders and grid graphs are solvable and, further, even the Cartesian product of two stars, which in a sense are the “most” unsolvable graphs.

s-strongly perfect cartesian product of graphs

1992 ◽  
Vol 16 (4) ◽  
pp. 297-303
Author(s):  
Elefterie Olaru ◽  
Eugen M??ndrescu
Keyword(s):  
Cartesian Product ◽  
Cartesian Product Of Graphs ◽  
Product Of Graphs

THE DIAMETER VARIABILITY OF THE CARTESIAN PRODUCT OF GRAPHS

2014 ◽  
Vol 06 (01) ◽  
pp. 1450001 ◽  
Author(s):  
M. R. CHITHRA ◽  
A. VIJAYAKUMAR
Keyword(s):  
Interconnection Networks ◽  
Cartesian Product ◽  
Graph Products ◽  
Single Edge ◽  
Cartesian Product Of Graphs ◽  
Product Of Graphs

The diameter of a graph can be affected by the addition or deletion of edges. In this paper, we examine the Cartesian product of graphs whose diameter increases (decreases) by the deletion (addition) of a single edge. The problems of minimality and maximality of the Cartesian product of graphs with respect to its diameter are also solved. These problems are motivated by the fact that most of the interconnection networks are graph products and a good network must be hard to disrupt and the transmissions must remain connected even if some vertices or edges fail.

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