A majority k-coloring of a digraph D with k colors is an assignment c:V(D)→{1,2,…,k},such that for every v∈V(D),we have c(w)=c(v)for at most half of all out-neighbors w∈N^(+)(v).For a natural number k≥2,a 1/k-maj...A majority k-coloring of a digraph D with k colors is an assignment c:V(D)→{1,2,…,k},such that for every v∈V(D),we have c(w)=c(v)for at most half of all out-neighbors w∈N^(+)(v).For a natural number k≥2,a 1/k-majority coloring of a digraph is a coloring of the vertices such that each vertex receives the same color as at most a 1/k proportion of its out-neighbours.Kreutzer,Oum,Seymour,van der Zypen and Wood proved that every digraph has a majority 4-coloring and conjectured that every digraph admits a majority 3-coloring.Gireao,Kittipassorn and Popielarz proved that every digraph has a 1/k-majority 2k-coloring and conjectured that every digraph admits a 1/k majority(2k-1)-coloring.We showed that every r-regular digraph D with r>36ln(2n)has a majority 3-coloring and proved that every digraph D with minimum outdegreeδ+>2k2(2k-1)/(k-1)^(2)ln2(n)[(2k-1)n]has a 1/k-majority(2k-1)-coloring.We showed that every r-regular digraph D with r>36ln(2n)has a majority 3-coloring and proved that every digraph D with minimum outdegreeδ+>,2k^(2)(2k-1)^(2)/(k-1)^(2)ln[(2k-1)n]has a 1/k-majority(2k-1)-coloring.And we also proved that every r-regular digraph D with r>3k^(2)(2k-1)/(k-1)^2ln(2n)has a 1/k-majority(2k-1)-coloring.展开更多
A linear directed forest is a directed graph in which every component is a directed path.The linear arboricity la(D) of a digraph D is the minimum number of linear directed forests in D whose union covers all arcs of ...A linear directed forest is a directed graph in which every component is a directed path.The linear arboricity la(D) of a digraph D is the minimum number of linear directed forests in D whose union covers all arcs of D. For every d-regular digraph D, Nakayama and P′eroche conjecture that la(D) = d + 1. In this paper, we consider the linear arboricity for complete symmetric digraphs,regular digraphs with high directed girth and random regular digraphs and we improve some wellknown results. Moreover, we propose a more precise conjecture about the linear arboricity for regular digraphs.展开更多
In this paper, we define a class of strongly connected digraph, called the k-walk- regular digraph, study some properties of it, provide its some algebraic characterization and point out that the 0-walk-regular digrap...In this paper, we define a class of strongly connected digraph, called the k-walk- regular digraph, study some properties of it, provide its some algebraic characterization and point out that the 0-walk-regular digraph is the same as the walk-regular digraph discussed by Liu and Lin in 2010 and the D-walk-regular digraph is identical with the weakly distance-regular digraph defined by Comellas et al in 2004.展开更多
基金Supported by the National Natural Science Foundation of China(Grant No.12071351)the Natural Science Foundation of Shandong Provence(Grant No.ZR2020MA043).
文摘A majority k-coloring of a digraph D with k colors is an assignment c:V(D)→{1,2,…,k},such that for every v∈V(D),we have c(w)=c(v)for at most half of all out-neighbors w∈N^(+)(v).For a natural number k≥2,a 1/k-majority coloring of a digraph is a coloring of the vertices such that each vertex receives the same color as at most a 1/k proportion of its out-neighbours.Kreutzer,Oum,Seymour,van der Zypen and Wood proved that every digraph has a majority 4-coloring and conjectured that every digraph admits a majority 3-coloring.Gireao,Kittipassorn and Popielarz proved that every digraph has a 1/k-majority 2k-coloring and conjectured that every digraph admits a 1/k majority(2k-1)-coloring.We showed that every r-regular digraph D with r>36ln(2n)has a majority 3-coloring and proved that every digraph D with minimum outdegreeδ+>2k2(2k-1)/(k-1)^(2)ln2(n)[(2k-1)n]has a 1/k-majority(2k-1)-coloring.We showed that every r-regular digraph D with r>36ln(2n)has a majority 3-coloring and proved that every digraph D with minimum outdegreeδ+>,2k^(2)(2k-1)^(2)/(k-1)^(2)ln[(2k-1)n]has a 1/k-majority(2k-1)-coloring.And we also proved that every r-regular digraph D with r>3k^(2)(2k-1)/(k-1)^2ln(2n)has a 1/k-majority(2k-1)-coloring.
基金Supported by NSFC(Grant Nos.11601093 and 11671296)
文摘A linear directed forest is a directed graph in which every component is a directed path.The linear arboricity la(D) of a digraph D is the minimum number of linear directed forests in D whose union covers all arcs of D. For every d-regular digraph D, Nakayama and P′eroche conjecture that la(D) = d + 1. In this paper, we consider the linear arboricity for complete symmetric digraphs,regular digraphs with high directed girth and random regular digraphs and we improve some wellknown results. Moreover, we propose a more precise conjecture about the linear arboricity for regular digraphs.
基金Supported by the National Natural Science Foundation of China (Grant Nos.1077105110971052)+2 种基金the National Natural Foundation of Hebei Province (Grant No.A2008000128)Educational Committee of Hebei Province(Grant No.2009134)Youth Science Foundation of Hebei Normal University (Grant No.L2008Q01)
文摘In this paper, we define a class of strongly connected digraph, called the k-walk- regular digraph, study some properties of it, provide its some algebraic characterization and point out that the 0-walk-regular digraph is the same as the walk-regular digraph discussed by Liu and Lin in 2010 and the D-walk-regular digraph is identical with the weakly distance-regular digraph defined by Comellas et al in 2004.
