{"title":"On products of strong Skolem starters","authors":"Oleg Ogandzhanyants, Margarita Kondratieva, Nabil Shalaby","doi":"10.1002/jcd.21943","DOIUrl":"10.1002/jcd.21943","url":null,"abstract":"<p>In 1991, Shalaby conjectured that any <span></span><math>\u0000 \u0000 <mrow>\u0000 <msub>\u0000 <mi>Z</mi>\u0000 \u0000 <mi>n</mi>\u0000 </msub>\u0000 </mrow></math>, where <span></span><math>\u0000 \u0000 <mrow>\u0000 <mi>n</mi>\u0000 \u0000 <mo>≡</mo>\u0000 \u0000 <mn>1</mn>\u0000 </mrow></math> or <span></span><math>\u0000 \u0000 <mrow>\u0000 <mn>3</mn>\u0000 <mspace></mspace>\u0000 \u0000 <mrow>\u0000 <mo>(</mo>\u0000 \u0000 <mrow>\u0000 <mi>mod</mi>\u0000 <mspace></mspace>\u0000 \u0000 <mn>8</mn>\u0000 </mrow>\u0000 \u0000 <mo>)</mo>\u0000 </mrow>\u0000 \u0000 <mo>,</mo>\u0000 \u0000 <mi>n</mi>\u0000 \u0000 <mo>≥</mo>\u0000 \u0000 <mn>11</mn>\u0000 </mrow></math>, admits a strong Skolem starter. In 2018, the authors fully described and explicitly constructed the infinite “cardioidal” family of strong Skolem starters. No other infinite family of these combinatorial designs was known to date. Statements regarding the products of starters, proven in this paper give a new way of generating strong or skew Skolem starters of composite orders. This approach extends our previous result by generating new infinite families of these starters that are not cardioidal.</p>","PeriodicalId":15389,"journal":{"name":"Journal of Combinatorial Designs","volume":"32 8","pages":"464-487"},"PeriodicalIF":0.7,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140942168","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"New results on large sets of orthogonal arrays and orthogonal arrays","authors":"Guangzhou Chen, Xiaodong Niu, Jiufeng Shi","doi":"10.1002/jcd.21944","DOIUrl":"10.1002/jcd.21944","url":null,"abstract":"<p>Orthogonal array and a large set of orthogonal arrays are important research objects in combinatorial design theory, and they are widely applied to statistics, computer science, coding theory, and cryptography. In this paper, some new series of large sets of orthogonal arrays are given by direct construction, juxtaposition construction, Hadamard construction, finite field construction, and difference matrix construction. Subsequently, many new infinite classes of orthogonal arrays are obtained by using these large sets of orthogonal arrays and Kronecker product.</p>","PeriodicalId":15389,"journal":{"name":"Journal of Combinatorial Designs","volume":"32 8","pages":"488-515"},"PeriodicalIF":0.7,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140930827","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"On equitably 2-colourable odd cycle decompositions","authors":"Andrea Burgess, Francesca Merola","doi":"10.1002/jcd.21937","DOIUrl":"10.1002/jcd.21937","url":null,"abstract":"<p>An <span></span><math>\u0000 \u0000 <mrow>\u0000 <mi>ℓ</mi>\u0000 </mrow></math>-cycle decomposition of <span></span><math>\u0000 \u0000 <mrow>\u0000 <msub>\u0000 <mi>K</mi>\u0000 \u0000 <mi>v</mi>\u0000 </msub>\u0000 </mrow></math> is said to be <i>equitably 2-colourable</i> if there is a 2-vertex-colouring of <span></span><math>\u0000 \u0000 <mrow>\u0000 <msub>\u0000 <mi>K</mi>\u0000 \u0000 <mi>v</mi>\u0000 </msub>\u0000 </mrow></math> such that each colour is represented (approximately) an equal number of times on each cycle: more precisely, we ask that in each cycle <span></span><math>\u0000 \u0000 <mrow>\u0000 <mi>C</mi>\u0000 </mrow></math> of the decomposition, each colour appears on <span></span><math>\u0000 \u0000 <mrow>\u0000 <mrow>\u0000 <mo>⌊</mo>\u0000 \u0000 <mrow>\u0000 <mi>ℓ</mi>\u0000 \u0000 <mo>∕</mo>\u0000 \u0000 <mn>2</mn>\u0000 </mrow>\u0000 \u0000 <mo>⌋</mo>\u0000 </mrow>\u0000 </mrow></math> or <span></span><math>\u0000 \u0000 <mrow>\u0000 <mrow>\u0000 <mo>⌈</mo>\u0000 \u0000 <mrow>\u0000 <mi>ℓ</mi>\u0000 \u0000 <mo>∕</mo>\u0000 \u0000 <mn>2</mn>\u0000 </mrow>\u0000 \u0000 <mo>⌉</mo>\u0000 </mrow>\u0000 </mrow></math> of the vertices of <span></span><math>\u0000 \u0000 <mrow>\u0000 <mi>C</mi>\u0000 </mrow></math>. In this paper we study the existence of equitably 2-colourable <span></span><math>\u0000 \u0000 <mrow>\u0000 <mi>ℓ</mi>\u0000 </mrow></math>-cycle decompositions of <span></span><math>\u0000 \u0000 <mrow>\u0000 <msub>\u0000 <mi>K</mi>\u0000 \u0000 <mi>v</mi>\u0000 </msub>\u0000 </mrow></math>, where <span></span><math>\u0000 \u0000 <mrow>\u0000 <mi>ℓ</mi>\u0000 </mrow></math> is odd, and prove the existence of such a decomposition for <span></span><math>\u0000 \u0000 <mrow>\u0000 <mi>v</mi>\u0000 \u0000 <mo>≡</mo>\u0000 \u0000 <mn>1</mn>\u0000 \u0000 <mo>,</mo>\u0000 \u0000 <mi>ℓ</mi>\u0000 </mrow></math> (mod <span></span><math>\u0000 \u0000 ","PeriodicalId":15389,"journal":{"name":"Journal of Combinatorial Designs","volume":"32 8","pages":"419-437"},"PeriodicalIF":0.7,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/jcd.21937","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140630988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Maximal cocliques and the chromatic number of the Kneser graph on chambers of PG\u0000 \u0000 \u0000 \u0000 (\u0000 \u0000 3\u0000 ,\u0000 q\u0000 \u0000 )\u0000 \u0000 \u0000 $(3,q)$","authors":"Philipp Heering, Klaus Metsch","doi":"10.1002/jcd.21940","DOIUrl":"10.1002/jcd.21940","url":null,"abstract":"<p>Let <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>Γ</mi>\u0000 </mrow>\u0000 <annotation> ${rm{Gamma }}$</annotation>\u0000 </semantics></math> be the graph whose vertices are the chambers of the finite projective 3-space <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mtext>PG</mtext>\u0000 <mrow>\u0000 <mo>(</mo>\u0000 <mrow>\u0000 <mn>3</mn>\u0000 <mo>,</mo>\u0000 <mi>q</mi>\u0000 </mrow>\u0000 <mo>)</mo>\u0000 </mrow>\u0000 </mrow>\u0000 <annotation> $text{PG}(3,q)$</annotation>\u0000 </semantics></math>, with two vertices being adjacent if and only if the corresponding chambers are in general position. We show that a maximal independent set of vertices of <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>Γ</mi>\u0000 </mrow>\u0000 <annotation> ${rm{Gamma }}$</annotation>\u0000 </semantics></math> contains <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msup>\u0000 <mi>q</mi>\u0000 <mn>4</mn>\u0000 </msup>\u0000 <mo>+</mo>\u0000 <mn>3</mn>\u0000 <msup>\u0000 <mi>q</mi>\u0000 <mn>3</mn>\u0000 </msup>\u0000 <mo>+</mo>\u0000 <mn>4</mn>\u0000 <msup>\u0000 <mi>q</mi>\u0000 <mn>2</mn>\u0000 </msup>\u0000 <mo>+</mo>\u0000 <mn>3</mn>\u0000 <mi>q</mi>\u0000 <mo>+</mo>\u0000 <mn>1</mn>\u0000 </mrow>\u0000 <annotation> ${q}^{4}+3{q}^{3}+4{q}^{2}+3q+1$</annotation>\u0000 </semantics></math>, or <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>3</mn>\u0000 <msup>\u0000 <mi>q</mi>\u0000 <mn>3</mn>\u0000 </msup>\u0000 <mo>+</mo>\u0000 <mn>5</mn>\u0000 <msup>\u0000 <mi>q</mi>\u0000 <mn>2</mn>\u0000 </msup>\u0000 <mo>+</mo>\u0000 <mn>3</mn>\u0000 <mi>q</mi>\u0000 <mo>+</mo>\u0000 <mn>1</mn>\u0000 </mrow>\u0000 <annotation> $3{q}^{3}+5{q}^{2}+3q+1$</annotation>\u0000 </semantics></math>, or at most <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>3</mn>\u0000 <msup>\u0000 <mi>","PeriodicalId":15389,"journal":{"name":"Journal of Combinatorial Designs","volume":"32 7","pages":"388-409"},"PeriodicalIF":0.7,"publicationDate":"2024-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/jcd.21940","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140570787","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}