{"title":"里氏群作为整块设计的自变群","authors":"Ashraf Daneshkhah","doi":"10.1016/j.exco.2024.100137","DOIUrl":null,"url":null,"abstract":"<div><p>A recent classification of flag-transitive 2-designs with parameters <span><math><mrow><mo>(</mo><mi>v</mi><mo>,</mo><mi>k</mi><mo>,</mo><mi>λ</mi><mo>)</mo></mrow></math></span> whose replication number <span><math><mi>r</mi></math></span> is coprime to <span><math><mi>λ</mi></math></span> gives rise to eight possible infinite families of 2-designs, some of which are with new parameters. In this note, we give explicit constructions for two of these families of 2-designs, and show that for a given positive integer <span><math><mrow><mi>q</mi><mo>=</mo><msup><mrow><mn>3</mn></mrow><mrow><mn>2</mn><mi>n</mi><mo>+</mo><mn>1</mn></mrow></msup><mo>⩾</mo><mn>27</mn></mrow></math></span>, there exist 2-designs with parameters <span><math><mrow><mo>(</mo><msup><mrow><mi>q</mi></mrow><mrow><mn>3</mn></mrow></msup><mo>+</mo><mn>1</mn><mo>,</mo><msup><mrow><mi>q</mi></mrow><mrow><mi>i</mi></mrow></msup><mo>,</mo><msup><mrow><mi>q</mi></mrow><mrow><mi>i</mi></mrow></msup><mo>−</mo><mn>1</mn><mo>)</mo></mrow></math></span>, for <span><math><mrow><mi>i</mi><mo>=</mo><mn>1</mn><mo>,</mo><mn>2</mn></mrow></math></span>, admitting the Ree group <span><math><mrow><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup><msub><mrow><mi>G</mi></mrow><mrow><mn>2</mn></mrow></msub><mrow><mo>(</mo><mi>q</mi><mo>)</mo></mrow></mrow></math></span> as their automorphism groups.</p></div>","PeriodicalId":100517,"journal":{"name":"Examples and Counterexamples","volume":"5 ","pages":"Article 100137"},"PeriodicalIF":0.0000,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S2666657X2400003X/pdfft?md5=874ac10905c9399343d40e6310933a30&pid=1-s2.0-S2666657X2400003X-main.pdf","citationCount":"0","resultStr":"{\"title\":\"Ree groups as automorphism groups of block designs\",\"authors\":\"Ashraf Daneshkhah\",\"doi\":\"10.1016/j.exco.2024.100137\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>A recent classification of flag-transitive 2-designs with parameters <span><math><mrow><mo>(</mo><mi>v</mi><mo>,</mo><mi>k</mi><mo>,</mo><mi>λ</mi><mo>)</mo></mrow></math></span> whose replication number <span><math><mi>r</mi></math></span> is coprime to <span><math><mi>λ</mi></math></span> gives rise to eight possible infinite families of 2-designs, some of which are with new parameters. In this note, we give explicit constructions for two of these families of 2-designs, and show that for a given positive integer <span><math><mrow><mi>q</mi><mo>=</mo><msup><mrow><mn>3</mn></mrow><mrow><mn>2</mn><mi>n</mi><mo>+</mo><mn>1</mn></mrow></msup><mo>⩾</mo><mn>27</mn></mrow></math></span>, there exist 2-designs with parameters <span><math><mrow><mo>(</mo><msup><mrow><mi>q</mi></mrow><mrow><mn>3</mn></mrow></msup><mo>+</mo><mn>1</mn><mo>,</mo><msup><mrow><mi>q</mi></mrow><mrow><mi>i</mi></mrow></msup><mo>,</mo><msup><mrow><mi>q</mi></mrow><mrow><mi>i</mi></mrow></msup><mo>−</mo><mn>1</mn><mo>)</mo></mrow></math></span>, for <span><math><mrow><mi>i</mi><mo>=</mo><mn>1</mn><mo>,</mo><mn>2</mn></mrow></math></span>, admitting the Ree group <span><math><mrow><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup><msub><mrow><mi>G</mi></mrow><mrow><mn>2</mn></mrow></msub><mrow><mo>(</mo><mi>q</mi><mo>)</mo></mrow></mrow></math></span> as their automorphism groups.</p></div>\",\"PeriodicalId\":100517,\"journal\":{\"name\":\"Examples and Counterexamples\",\"volume\":\"5 \",\"pages\":\"Article 100137\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"2024-02-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"https://www.sciencedirect.com/science/article/pii/S2666657X2400003X/pdfft?md5=874ac10905c9399343d40e6310933a30&pid=1-s2.0-S2666657X2400003X-main.pdf\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Examples and Counterexamples\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S2666657X2400003X\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Examples and Counterexamples","FirstCategoryId":"1085","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S2666657X2400003X","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
Ree groups as automorphism groups of block designs
A recent classification of flag-transitive 2-designs with parameters whose replication number is coprime to gives rise to eight possible infinite families of 2-designs, some of which are with new parameters. In this note, we give explicit constructions for two of these families of 2-designs, and show that for a given positive integer , there exist 2-designs with parameters , for , admitting the Ree group as their automorphism groups.