Lijun Ji , Dehai Liu , Kaishun Wang , Tian Yao , Shuhui Yu
{"title":"向量空间的s-几乎t相交族","authors":"Lijun Ji , Dehai Liu , Kaishun Wang , Tian Yao , Shuhui Yu","doi":"10.1016/j.disc.2025.114661","DOIUrl":null,"url":null,"abstract":"<div><div>Let <em>V</em> be a finite dimensional vector space over a finite field, and <span><math><mi>F</mi></math></span> a family consisting of <em>k</em>-subspaces of <em>V</em>. The family <span><math><mi>F</mi></math></span> is called <em>t</em>-intersecting if <span><math><mi>dim</mi><mo></mo><mo>(</mo><mi>F</mi><mo>∩</mo><msup><mrow><mi>F</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>)</mo><mo>≥</mo><mi>t</mi></math></span> for any <span><math><mi>F</mi><mo>,</mo><msup><mrow><mi>F</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>∈</mo><mi>F</mi></math></span>. We say <span><math><mi>F</mi></math></span> is <em>s</em>-almost <em>t</em>-intersecting if <span><math><mrow><mo>|</mo><mrow><mo>{</mo><mi>F</mi><mo>∈</mo><mi>F</mi><mo>:</mo><mi>dim</mi><mo></mo><mo>(</mo><mi>F</mi><mo>∩</mo><msup><mrow><mi>F</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>)</mo><mo><</mo><mi>t</mi><mo>}</mo></mrow><mo>|</mo></mrow><mo>≤</mo><mi>s</mi></math></span> for any <span><math><msup><mrow><mi>F</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>∈</mo><mi>F</mi></math></span>. In this paper, we prove that <em>s</em>-almost <em>t</em>-intersecting families with maximum size are <em>t</em>-intersecting. We also consider <em>s</em>-almost <em>t</em>-intersecting families which are not <em>t</em>-intersecting, and characterize such families with maximum size for <span><math><mo>(</mo><mi>s</mi><mo>,</mo><mi>t</mi><mo>)</mo><mo>≠</mo><mo>(</mo><mn>1</mn><mo>,</mo><mn>1</mn><mo>)</mo></math></span> and <span><math><mi>k</mi><mo>≥</mo><mi>t</mi><mo>+</mo><mn>2</mn></math></span>. The results for 1-almost 1-intersecting families provided by Shan and Zhou are generalized.</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"349 1","pages":"Article 114661"},"PeriodicalIF":0.7000,"publicationDate":"2025-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"s-almost t-intersecting families for vector spaces\",\"authors\":\"Lijun Ji , Dehai Liu , Kaishun Wang , Tian Yao , Shuhui Yu\",\"doi\":\"10.1016/j.disc.2025.114661\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><div>Let <em>V</em> be a finite dimensional vector space over a finite field, and <span><math><mi>F</mi></math></span> a family consisting of <em>k</em>-subspaces of <em>V</em>. The family <span><math><mi>F</mi></math></span> is called <em>t</em>-intersecting if <span><math><mi>dim</mi><mo></mo><mo>(</mo><mi>F</mi><mo>∩</mo><msup><mrow><mi>F</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>)</mo><mo>≥</mo><mi>t</mi></math></span> for any <span><math><mi>F</mi><mo>,</mo><msup><mrow><mi>F</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>∈</mo><mi>F</mi></math></span>. We say <span><math><mi>F</mi></math></span> is <em>s</em>-almost <em>t</em>-intersecting if <span><math><mrow><mo>|</mo><mrow><mo>{</mo><mi>F</mi><mo>∈</mo><mi>F</mi><mo>:</mo><mi>dim</mi><mo></mo><mo>(</mo><mi>F</mi><mo>∩</mo><msup><mrow><mi>F</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>)</mo><mo><</mo><mi>t</mi><mo>}</mo></mrow><mo>|</mo></mrow><mo>≤</mo><mi>s</mi></math></span> for any <span><math><msup><mrow><mi>F</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>∈</mo><mi>F</mi></math></span>. In this paper, we prove that <em>s</em>-almost <em>t</em>-intersecting families with maximum size are <em>t</em>-intersecting. We also consider <em>s</em>-almost <em>t</em>-intersecting families which are not <em>t</em>-intersecting, and characterize such families with maximum size for <span><math><mo>(</mo><mi>s</mi><mo>,</mo><mi>t</mi><mo>)</mo><mo>≠</mo><mo>(</mo><mn>1</mn><mo>,</mo><mn>1</mn><mo>)</mo></math></span> and <span><math><mi>k</mi><mo>≥</mo><mi>t</mi><mo>+</mo><mn>2</mn></math></span>. The results for 1-almost 1-intersecting families provided by Shan and Zhou are generalized.</div></div>\",\"PeriodicalId\":50572,\"journal\":{\"name\":\"Discrete Mathematics\",\"volume\":\"349 1\",\"pages\":\"Article 114661\"},\"PeriodicalIF\":0.7000,\"publicationDate\":\"2025-07-07\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Discrete Mathematics\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0012365X25002699\",\"RegionNum\":3,\"RegionCategory\":\"数学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"MATHEMATICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Discrete Mathematics","FirstCategoryId":"100","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0012365X25002699","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATHEMATICS","Score":null,"Total":0}
s-almost t-intersecting families for vector spaces
Let V be a finite dimensional vector space over a finite field, and a family consisting of k-subspaces of V. The family is called t-intersecting if for any . We say is s-almost t-intersecting if for any . In this paper, we prove that s-almost t-intersecting families with maximum size are t-intersecting. We also consider s-almost t-intersecting families which are not t-intersecting, and characterize such families with maximum size for and . The results for 1-almost 1-intersecting families provided by Shan and Zhou are generalized.
期刊介绍:
Discrete Mathematics provides a common forum for significant research in many areas of discrete mathematics and combinatorics. Among the fields covered by Discrete Mathematics are graph and hypergraph theory, enumeration, coding theory, block designs, the combinatorics of partially ordered sets, extremal set theory, matroid theory, algebraic combinatorics, discrete geometry, matrices, and discrete probability theory.
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