{"title":"排列幂的下降","authors":"Kassie Archer, Aaron Geary","doi":"10.1016/j.disc.2025.114551","DOIUrl":null,"url":null,"abstract":"<div><div>We consider a few special cases of the more general question: How many permutations <span><math><mi>π</mi><mo>∈</mo><msub><mrow><mi>S</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> have the property that <span><math><msup><mrow><mi>π</mi></mrow><mrow><mn>2</mn></mrow></msup></math></span> has <em>j</em> descents for some <em>j</em>? In this paper, we first enumerate Grassmannian permutations <em>π</em> by the number of descents in <span><math><msup><mrow><mi>π</mi></mrow><mrow><mn>2</mn></mrow></msup></math></span>. We then consider all permutations whose square has exactly one descent, fully enumerating when the descent is “small” and providing a lower bound in the general case. Finally, we enumerate permutations whose square or cube has the maximum number of descents, and finish the paper with a few future directions for study.</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"348 9","pages":"Article 114551"},"PeriodicalIF":0.7000,"publicationDate":"2025-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Descents in powers of permutations\",\"authors\":\"Kassie Archer, Aaron Geary\",\"doi\":\"10.1016/j.disc.2025.114551\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><div>We consider a few special cases of the more general question: How many permutations <span><math><mi>π</mi><mo>∈</mo><msub><mrow><mi>S</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> have the property that <span><math><msup><mrow><mi>π</mi></mrow><mrow><mn>2</mn></mrow></msup></math></span> has <em>j</em> descents for some <em>j</em>? In this paper, we first enumerate Grassmannian permutations <em>π</em> by the number of descents in <span><math><msup><mrow><mi>π</mi></mrow><mrow><mn>2</mn></mrow></msup></math></span>. We then consider all permutations whose square has exactly one descent, fully enumerating when the descent is “small” and providing a lower bound in the general case. Finally, we enumerate permutations whose square or cube has the maximum number of descents, and finish the paper with a few future directions for study.</div></div>\",\"PeriodicalId\":50572,\"journal\":{\"name\":\"Discrete Mathematics\",\"volume\":\"348 9\",\"pages\":\"Article 114551\"},\"PeriodicalIF\":0.7000,\"publicationDate\":\"2025-04-24\",\"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/S0012365X25001591\",\"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/S0012365X25001591","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATHEMATICS","Score":null,"Total":0}
We consider a few special cases of the more general question: How many permutations have the property that has j descents for some j? In this paper, we first enumerate Grassmannian permutations π by the number of descents in . We then consider all permutations whose square has exactly one descent, fully enumerating when the descent is “small” and providing a lower bound in the general case. Finally, we enumerate permutations whose square or cube has the maximum number of descents, and finish the paper with a few future directions for study.
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.
Items in the journal include research articles (Contributions or Notes, depending on length) and survey/expository articles (Perspectives). Efforts are made to process the submission of Notes (short articles) quickly. The Perspectives section features expository articles accessible to a broad audience that cast new light or present unifying points of view on well-known or insufficiently-known topics.