研究生: |
蕭衡慶 Heng-ching Hsiao |
---|---|
論文名稱: |
正交群的多項式不變量 Polynomial Invariants of Orthogonal Groups |
指導教授: |
洪有情
Hung, Yu-Ching |
學位類別: |
碩士 Master |
系所名稱: |
數學系 Department of Mathematics |
論文出版年: | 2007 |
畢業學年度: | 95 |
語文別: | 英文 |
論文頁數: | 34 |
中文關鍵詞: | 二次型 、正交群 、不變子環 |
英文關鍵詞: | quadratic form, orthogonal group, invariant subring |
論文種類: | 學術論文 |
相關次數: | 點閱:136 下載:14 |
分享至: |
查詢本校圖書館目錄 查詢臺灣博碩士論文知識加值系統 勘誤回報 |
這篇論文主要的結果是希望具體描述“正交群作用在佈於有限體的多項式環上其不變子環的生成元”。首先我們在不變子環裡找出若干元素,去證明不變子環is integral over這些元素所生成的子環(我們記為R_{n}^{*}),並且證明了不變子環與R_{n}^{*}有相同的商體;最後我們證明了當n=2,4時,R_{n}^{*}是一個UFD,因此R_{n}^{*} is integrally closed,所以我們可以得知不變子環在n=2,4時的生成元。所謂正交群是指保持二次型之所有可逆線性變換中所構成的乘法群;在此篇論文中,我們特別強調此二次型為Q_{n}^{-}=x_{1}^{2}-x_{2}^{2}+...+x_{n-1}^{2}-εx_{n}^{2},其中n是偶數且ε是一個在有限體裡的非平方數。
Let Q_{n}^{-}=x_{1}^{2}-x_{2}^{2}+...+x_{n-1}^{2}-εx_{n}^{2}
be a nondegenerate quadratic form over the
finite field Fq with charFq is not equal to 2 where ε is a non-square in Fq, and let O(Fq^{n},Q_{n}^{-}) be the associated orthogonal group. Let O(Fq^{n},Q_{n}^{-}) act linearly on the polynomial ring
Fq[x_{1},...,x_{n}]. In this thesis we try to find the invariant subring Fq[x_{1},...,x_{n}]^{O(Fq^{n},Q_{n}^{-})}
with explicit generators. In fact, we find the invariant elements in Fq[x_{1},...,x_{n}]^{O(Fq^{n},Q_{n}^{-})},
and denote the subring which these invariant elements generate by R_{n}^{*}. We show that
Fq[x_{1},...,x_{n}]^{O(Fq^{n},Q_{n}^{-})} is integral over R_{n}^{*}, and show that Fq[x_{1},...,x_{n}]^{O(Fq^{n},Q_{n}^{-})} and R_{n}^{*} have the same quotient field. As n=2,4, we show that R_{n}^{*} is a UFD, and hence is
integrally closed. Thus Fq[x1,x2]^{O(Fq^{2},Q_{2}^{-})}=R_{2}^{*} and Fq[x1,x2,x3,x4]]^{O(Fq^{4},Q_{4}^{-})}=R_{4}^{*}, so we get the generators of invariant subring when n=2,4.
[1] M.F Atiyah and I.G. Macdonald,Introduction to Commutative Algebra. Addison-Wesley Reading, Mass., 1969.
[2] N. Jacobson, Basic algebra Vol.I. W. H. Freeman and Comp, 1984.
[3] H. Chu, Polynomial invariants of four-dimensional orthogonal groups. Communication in Algebra 29 (2001), 1153-1164.
[4] H. Chu, Orthogonal group actions on rational function fields. Bull. Inst. Math. Acad. Sinica. 16 (1988), 115-122.
[5] S. D. Cohen, Rational functions invariant under an orthogonal group. Bull. London Math. Soc. 22 (1990), 217-221.
[6] D. Carlisle and P. Kropholler, Rational invariants of certain orthogonal and unitary groups. Bull. London Math. Soc. 24 (1992), 57-60.
[7] Chan-Hung Tung, On polynomial invariants of orthogonal group actions. Thesis for Master degree, Department of Mathematics, National Taiwan Normal University,2004.
[8] Shin-Yao Jow, Polynomial invariants of finite unitary groups. Thesis for Master degree, Department of Mathematics, National Taiwan University, 2002.
[9] L. Chiang and Y.C. Hung, The invariants of orthogonal group actions. Bull. Astralian Math. Soc. 48 (1993), 313-319.
[10] D. Eisenbud, Commutative algebra with a view toward algebraic geometry. Graduate Texts in Mathematics 150, Springer-verlag, 1994.
[11] I. Kaplansky, Communicative Ring. The University of Chicago Press:Chicago, 1974.
[12] R. Y. Sharp, Steps in Commutative Algebra. Cambridge University Press, 2000.