Vek zhivi vek uchis', ili chislo 6
Nov. 29th, 2002 12:54 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
posicOkazyvaetsya, gruppa perestanovok 6-elementnogo mnozhestva imeet vneshnij avtomorfizm. Ya prochital ob etom zdes':
Consider 6 things, e.g. the numerals 123456. There are 15 non-ordered pairs of them. (Call these "duads.") Also there are 15 ways to divide the original set into three duads, e.g. {(12}{34}{56}}. Call these "synthemes." Five synthemes can be chosen so as to contain each duad exactly once; and there turn out to be exactly six ways to make this choice. You can label these six sets ABCDEF. Then a permutation of 123456 induces a permutation of ABCDEF. A two-cycle such as (12) induces a product of three disjoint two-cycles such as (AB)(CD)(EF), so the map from one permutation to the other cannot be an inner automorphism.
Dovol'no zamyslovataya vse-taki konstrukciya, sopostavlyayuschaya 6-elementnomu mnozhestvu drugoe 6-elementnoe mnozhestvo. Ya esche znayu na etu temu gorazdo bolee prostuyu konstrukciyu, sopostavlyayuschuyu 4-elementnomu mnozhestvu 3-elementnoe mnozhestvo.
Ostal'nye gruppy Sn (pri n ne ravnom 6) vneshnih avtomorfizmov ne imeyut, chto netrudno dokazat', rassmotrev klass sopryazhennosti, sostoyaschij iz transpozicij, i ego obraz pri nashem avtomorfizme. Podrobnosti imeyutsya zdes' (fajl v formate postscript).
Consider 6 things, e.g. the numerals 123456. There are 15 non-ordered pairs of them. (Call these "duads.") Also there are 15 ways to divide the original set into three duads, e.g. {(12}{34}{56}}. Call these "synthemes." Five synthemes can be chosen so as to contain each duad exactly once; and there turn out to be exactly six ways to make this choice. You can label these six sets ABCDEF. Then a permutation of 123456 induces a permutation of ABCDEF. A two-cycle such as (12) induces a product of three disjoint two-cycles such as (AB)(CD)(EF), so the map from one permutation to the other cannot be an inner automorphism.
Dovol'no zamyslovataya vse-taki konstrukciya, sopostavlyayuschaya 6-elementnomu mnozhestvu drugoe 6-elementnoe mnozhestvo. Ya esche znayu na etu temu gorazdo bolee prostuyu konstrukciyu, sopostavlyayuschuyu 4-elementnomu mnozhestvu 3-elementnoe mnozhestvo.
Ostal'nye gruppy Sn (pri n ne ravnom 6) vneshnih avtomorfizmov ne imeyut, chto netrudno dokazat', rassmotrev klass sopryazhennosti, sostoyaschij iz transpozicij, i ego obraz pri nashem avtomorfizme. Podrobnosti imeyutsya zdes' (fajl v formate postscript).
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Re: Через 3 года
Date: 2005-09-27 02:00 pm (UTC)возьмем матрицу М вышеуказанной симплектической формы, тогда
МХМ^{-1}=(X^{-1})^T, просто потому, что Х сохраняет скалярное произведение, определенное М, то есть Х^Т М Х = М.
Внешний автоморфизм группы Sp_4(F_2) должен переставлять две максимальные параболики разных типов, которые соответствуют какому–либо флагу (точка/изотропная прямая).