{"title":"A note on bipartite graphs whose [1,k]-domination number equal to their number of vertices","authors":"N. Ghareghani, Iztok Peterin, P. Sharifani","doi":"10.7494/opmath.2020.40.3.375","DOIUrl":"https://doi.org/10.7494/opmath.2020.40.3.375","url":null,"abstract":"A subset $D$ of the vertex set $V$ of a graph $G$ is called an $[1,k]$-dominating set if every vertex from $V-D$ is adjacent to at least one vertex and at most $k$ vertices of $D$. A $[1,k]$-dominating set with the minimum number of vertices is called a $gamma_{[1,k]}$-set and the number of its vertices is the $[1,k]$-domination number $gamma_{[1,k]}(G)$ of $G$. In this short note we show that the decision problem whether $gamma_{[1,k]}(G)=n$ is an $NP$-hard problem, even for bipartite graphs. Also, a simple construction of a bipartite graph $G$ of order $n$ satisfying $gamma_{[1,k]}(G)=n$ is given for every integer $ngeq (k+1)(2k+3)$.","PeriodicalId":8442,"journal":{"name":"arXiv: Combinatorics","volume":"128 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79555316","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"A combinatorial construction for two formulas in Slater’s list","authors":"Kagan Kursungöz","doi":"10.1142/s1793042120400114","DOIUrl":"https://doi.org/10.1142/s1793042120400114","url":null,"abstract":"We set up a combinatorial framework for inclusion-exclusion on the partitions into distinct parts to obtain an alternative generating function of partitions into distinct and non-consecutive parts. In connection with Rogers-Ramanujan identities, the generating function yields two formulas in Slater's list. The same formulas were constructed by Hirschhorn. We also use staircases to give alternative triple series for partitions into $d-$distinct parts for any $d geq 2$.","PeriodicalId":8442,"journal":{"name":"arXiv: Combinatorics","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79807477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"A construction of pairs of non-commutative rank 8 association schemes from non-symmetric rank 3 association schemes","authors":"A. Hanaki, Masayoshi Yoshikawa","doi":"10.5802/alco.167","DOIUrl":"https://doi.org/10.5802/alco.167","url":null,"abstract":"We construct a pair of non-commutative rank 8 association schemes from a rank 3 non-symmetric association scheme. For the pair, two association schemes have the same character table but different Frobenius-Schur indicators. This situation is similar to the pair of the dihedral group and the quaternion group of order 8. We also determine the structures of adjacency algebras of them over the rational number field.","PeriodicalId":8442,"journal":{"name":"arXiv: Combinatorics","volume":"119 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73493211","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"What is the Perfect Shuffle","authors":"James Enouen","doi":"10.1090/spec/022/01","DOIUrl":"https://doi.org/10.1090/spec/022/01","url":null,"abstract":"When shuffling a deck of cards, one probably wants to make sure it is thoroughly shuffled. A way to do this is by sifting through the cards to ensure that no adjacent cards are the same number, because surely this is a poorly shuffled deck. Unfortunately, human intuition for probability tends to lead us astray. For a standard 52-card deck of playing cards, the event is actually extremely likely. This report will attempt to elucidate how to answer this surprisingly difficult combinatorial question directly using rook polynomials.","PeriodicalId":8442,"journal":{"name":"arXiv: Combinatorics","volume":"8 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83434892","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Abstract 3-Rigidity and Bivariate $C_2^1$-Splines II: Combinatorial Characterization.","authors":"K. Clinch, B. Jackson, Shin-ichi Tanigawa","doi":"10.19086/da.34692","DOIUrl":"https://doi.org/10.19086/da.34692","url":null,"abstract":"We showed in the first paper of this series that the generic $C_2^1$-cofactor matroid is the unique maximal abstract $3$-rigidity matroid. In this paper we obtain a combinatorial characterization of independence in this matroid. This solves the cofactor counterpart of the combinatorial characterization problem for the rigidity of generic 3-dimensional bar-joint frameworks. We use our characterization to verify that the counterparts of conjectures of Dress (on the rank function) and Lov'{a}sz and Yemini (which suggested a sufficient connectivity condition for rigidity) hold for this matroid.","PeriodicalId":8442,"journal":{"name":"arXiv: Combinatorics","volume":"37 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85961551","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Abstract 3-Rigidity and Bivariate $C_2^1$-Splines I: Whiteley's Maximality Conjecture","authors":"K. Clinch, B. Jackson, Shin-ichi Tanigawa","doi":"10.19086/da.34691","DOIUrl":"https://doi.org/10.19086/da.34691","url":null,"abstract":"A long-standing conjecture in rigidity theory states that the generic 3-dimensional rigidity matroid is the unique maximal abstract 3-rigidity matroid (with respect to the weak order on matroids). Based on a close similarity between the generic 3-dimensional rigidity matroid and the generic $C_2^1$-cofactor matroid from approximation theory, Whiteley made an analogous conjecture in 1996 that the generic $C_2^1$-cofactor matroid is the unique maximal abstract 3-rigidity matroid. We verify Whiteley's conjecture in this paper. A key step in our proof is to verify a second conjecture of Whiteley that the `double V-replacement operation' preserves independence in the generic $C_2^1$-cofactor matroid.","PeriodicalId":8442,"journal":{"name":"arXiv: Combinatorics","volume":"16 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85278796","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Simple graphs of order 12 and minimum degree\u00006 contain K6 minors","authors":"Ryan Odeneal, Andrei Pavelescu","doi":"10.2140/involve.2020.13.829","DOIUrl":"https://doi.org/10.2140/involve.2020.13.829","url":null,"abstract":"We prove that every simple graph of order 12 which has minimum degree 6 contains a K_6 minor.","PeriodicalId":8442,"journal":{"name":"arXiv: Combinatorics","volume":"68 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84960230","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}