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词汇 Torsion subgroup
分类 英语词汇 英语翻译词典
释义

Torsion subgroup

中文百科

挠子群

在群论中,一个阿贝尔群 A挠子群定义为

A_T := \{a \in A : \exists n \in \N, \; na=0 \}

换言之,即 A 中的有限阶元素。根据 A 的交换性可知其为子群,此群有时也记为 \mathrm{Tor}(A)

同理,对任一素数 p,可定义 p-挠子群

A_{T_p} := \{a \in A : \exists n \in \N, \; p^n a=0 \}

挠子群可以表为 p-挠子群之直和:A_T = \bigoplus_p A_{T_p}。若 A 为有限群,则 A_{T_p} 是其唯一的 p-西洛子群。

满足 A_T = A 的阿贝尔群称作挠群周期群。若满足 A_T = (0),则称之为无挠群A/A_T 必无挠。

对于有限生成的阿贝尔群 AA_T 为其直和项,即:存在另一子群(未必唯一)B \subset A 使得 A = A_T \oplus B

英语百科

Torsion subgroup 挠子群

The 4-torsion subgroup of the quotient group of the complex numbers under addition by a lattice.

In the theory of abelian groups, the torsion subgroup AT of an abelian group A is the subgroup of A consisting of all elements that have finite order (the torsion elements of A). An abelian group A is called a torsion (or periodic) group if every element of A has finite order and is called torsion-free if every element of A except the identity is of infinite order.

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