Skew-rank of an oriented graph and independence number of its underlying graph

Xueliang Li () and Wen Xia ()
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Xueliang Li: Nankai University
Wen Xia: Nankai University

Journal of Combinatorial Optimization, 2019, vol. 38, issue 1, No 15, 268-277

Abstract: Abstract An oriented graph $$G^\sigma $$ G σ is a digraph which is obtained by orienting every edge of a simple graph G, where G is called the underlying graph of $$G^\sigma $$ G σ . Let $$S(G^\sigma )$$ S ( G σ ) denote the skew-adjacency matrix of $$G^\sigma $$ G σ and $$\alpha (G)$$ α ( G ) be the independence number of G. The rank of $$S(G^\sigma )$$ S ( G σ ) is called the skew-rank of $$G^\sigma $$ G σ , denoted by $$sr(G^\sigma )$$ s r ( G σ ) . Wong et al. studied the relation between the skew-rank of an oriented graph and the rank of its underlying graphs. Huang et al. recently studied the relationship between the skew-rank of an oriented graph and the independence number of its underlying graph, by giving some lower bounds for the sum, difference and quotient etc. They left over some questions for further studying the upper bounds of these parameters. In this paper, we extend this study by showing that $$sr(G^\sigma )+ 2\alpha (G) \le 2n$$ s r ( G σ ) + 2 α ( G ) ≤ 2 n , where n is the order of G, and two classes of oriented graphs are given to show that the upper bound 2n can be achieved. Furthermore, we answer some open questions by obtaining sharp upper bounds for $$sr(G^\sigma ) + \alpha (G)$$ s r ( G σ ) + α ( G ) , $$sr(G^\sigma ) - \alpha (G)$$ s r ( G σ ) - α ( G ) and $$sr(G^\sigma ) / \alpha (G)$$ s r ( G σ ) / α ( G ) .

Keywords: Skew-rank; Oriented graph; Oddly-oriented; Independence number; 05C50 (search for similar items in EconPapers)
Date: 2019
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DOI: 10.1007/s10878-019-00382-5

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