数学代写|现代代数代写Modern Algebra代考|Cyclic Groups

Doug I. Jones

Doug I. Jones

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数学代写|现代代数代写Modern Algebra代考|Cyclic Groups

数学代写|现代代数代写Modern Algebra代考|Cyclic Groups

In the last section, a group $G$ was defined to be cyclic if there exists an element $a \in G$ such that $G=\langle a\rangle$. It may happen that there is more than one element $a \in G$ such that $G=\langle a\rangle$. For the additive group $\mathbf{Z}$, we have $\mathbf{Z}=\langle 1\rangle$ and also $\mathbf{Z}=\langle-1\rangle$, since any $n \in \mathbf{Z}$ can be written as $(-n)(-1)$. Here, $(-n)(-1)$ does not indicate a product but rather a multiple of -1 , as described in Section 3.2.
Generator
Any element $a$ of the group $G$ such that $G=\langle a\rangle$ is a generator of $G$.
If $a$ is a generator of a multiplicative group $G$, then $a^{-1}$ is also, since any element $x \in G$ can be written as
$$
x=a^n=\left(a^{-1}\right)^{-n}
$$
for some integer $n$, and $G=\langle a\rangle=\left\langle a^{-1}\right\rangle$. For the additive group $G$, if $a$ is a generator of $G$, then $-a$ is also, since any $x \in G$ can be written as
$$
x=n a=(-n)(-a)
$$
for some integer $n$, and $G=\langle a\rangle=\langle-a\rangle$.

Example 1 The additive group
$$
\mathbf{Z}_n={[0],[1], \ldots,[n-1]}
$$
is a cyclic group with generator [1], since any $[k]$ in $\mathbf{Z}_n$ can be written as
$$
[k]=k[1]
$$
where $k[1]$ indicates a multiple of [1] as described in Section 3.2. Elements other than [1] may also be generators. To illustrate this, consider the particular case
$$
\mathbf{Z}_6={[0],[1],[2],[3],[4],[5]} .
$$
The element [5] is also a generator of $\mathbf{Z}_6$ since [5] is the additive inverse of [1]. The following list shows how $\mathbf{Z}_6$ is generated by [5]-that is, how $\mathbf{Z}_6$ consists of multiples of [5].
$$
\begin{aligned}
& 1[5]=[5] \
& 2[5]=[5]+[5]=[4] \
& 3[5]=[5]+[5]+[5]=[3] \
& 4[5]=[2] \
& 5[5]=[1] \
& 6[5]=[0]
\end{aligned}
$$
The cyclic subgroups generated by the other elements of $\mathbf{Z}_6$ under addition are
$$
\begin{aligned}
& \langle[0]\rangle={[0]} \
& \langle[2]\rangle={[2],[4],[0]} \
& \langle[3]\rangle={[3],[0]} \
& \langle[4]\rangle={[4],[2],[0]}=\langle[2]\rangle .
\end{aligned}
$$
Thus [1] and [5] are the only elements that are generators of the entire group.

数学代写|现代代数代写Modern Algebra代考|Generators of a Finite Cyclic Group

Let $G=\langle a\rangle$ be a cyclic group of order $n$. Then $a^m$ is a generator of $G$ if and only if $m$ and $n$ are relatively prime.
$p \Leftarrow q$ Proof On the one hand, if $m$ is such that $m$ and $n$ are relatively prime, then $d=$ $(m, n)=1$, and $a^m$ is a generator of $G$ by Theorem 3.26.
$p \Rightarrow q \quad$ On the other hand, if $a^m$ is a generator of $G$, then $a=\left(a^m\right)^p$ for some integer $p$. By part b of Theorem 3.21, this implies that $1 \equiv m p(\bmod n)$. That is,
$$
1-m p=n q
$$
for some integer $q$. This gives
$$
1=m p+n q,
$$
and it follows from Theorem 2.12 that $(m, n)=1$.

The Euler phi-function $\phi(n)$ was defined for positive integers $n$ in Exercise 23 of Section 2.8 as follows: $\phi(n)$ is the number of positive integers $m$ such that $1 \leq m \leq n$ and $(m, n)=1$. It follows, from Theorems 3.21 and 3.28, that the cyclic group $\langle a\rangle$ of order $n$ has $\phi(n)$ distinct generators.

Example 9 Let $G=\langle a\rangle$ be a cyclic group of order 10. The positive integers less than 10 and relatively prime to 10 are $1,3,7$, and 9 . Therefore, all generators of $G$ are included in the list
$a, a^3, a^7$, and $a^9$, and $G$ has $\phi(10)=4$ distinct generators.

数学代写|现代代数代写Modern Algebra代考|Cyclic Groups

现代代数代考

数学代写|现代代数代写Modern Algebra代考|Cyclic Groups

在上一节中,如果存在一个元素$a \in G$使得$G=\langle a\rangle$,则将组$G$定义为循环的。它可能发生,有多个元素$a \in G$这样$G=\langle a\rangle$。对于加性组$\mathbf{Z}$,我们有$\mathbf{Z}=\langle 1\rangle$和$\mathbf{Z}=\langle-1\rangle$,因为任何$n \in \mathbf{Z}$都可以写成$(-n)(-1)$。这里,$(-n)(-1)$并不表示一个乘积,而是-1的倍数,如3.2节所述。
发电机
组$G$中的任何元素$a$,使得$G=\langle a\rangle$是$G$的生成器。
如果$a$是乘法组$G$的生成器,那么$a^{-1}$也是,因为任何元素$x \in G$都可以写成
$$
x=a^n=\left(a^{-1}\right)^{-n}
$$
对于某个整数$n$和$G=\langle a\rangle=\left\langle a^{-1}\right\rangle$。对于添加组$G$,如果$a$是$G$的生成器,那么$-a$也是,因为任何$x \in G$都可以写成
$$
x=n a=(-n)(-a)
$$
对于某个整数$n$和$G=\langle a\rangle=\langle-a\rangle$。

示例1添加组
$$
\mathbf{Z}_n={[0],[1], \ldots,[n-1]}
$$
是一个具有生成器[1]的循环群,因为$\mathbf{Z}_n$中的任何$[k]$都可以写成
$$
[k]=k[1]
$$
其中$k[1]$表示3.2节中描述的[1]的倍数。除[1]以外的元素也可以是生成器。为了说明这一点,考虑一个特殊的案例
$$
\mathbf{Z}_6={[0],[1],[2],[3],[4],[5]} .
$$
元素[5]也是$\mathbf{Z}_6$的生成器,因为[5]是[1]的加性逆。下面的列表显示了[5]如何生成$\mathbf{Z}_6$,也就是说,$\mathbf{Z}_6$是如何由[5]的倍数组成的。
$$
\begin{aligned}
& 1[5]=[5] \
& 2[5]=[5]+[5]=[4] \
& 3[5]=[5]+[5]+[5]=[3] \
& 4[5]=[2] \
& 5[5]=[1] \
& 6[5]=[0]
\end{aligned}
$$
$\mathbf{Z}_6$的其他元素在加法作用下生成的循环子群为
$$
\begin{aligned}
& \langle[0]\rangle={[0]} \
& \langle[2]\rangle={[2],[4],[0]} \
& \langle[3]\rangle={[3],[0]} \
& \langle[4]\rangle={[4],[2],[0]}=\langle[2]\rangle .
\end{aligned}
$$
因此,[1]和[5]是整个组的唯一生成元素。

数学代写|现代代数代写Modern Algebra代考|Generators of a Finite Cyclic Group

让 $G=\langle a\rangle$ 是有序的循环群 $n$. 然后 $a^m$ 是的生成器 $G$ 当且仅当 $m$ 和 $n$ 都是相对优质的。
$p \Leftarrow q$ 证据一方面,如果 $m$ 是这样的 $m$ 和 $n$ 是相对优质的吗 $d=$ $(m, n)=1$,和 $a^m$ 是的生成器 $G$ 根据定理3.26。
$p \Rightarrow q \quad$ 另一方面,如果 $a^m$ 是的生成器 $G$那么, $a=\left(a^m\right)^p$ 对于某个整数 $p$. 根据定理3.21的b部分,这意味着 $1 \equiv m p(\bmod n)$. 也就是说,
$$
1-m p=n q
$$
对于某个整数 $q$. 这给出了
$$
1=m p+n q,
$$
由定理2.12可知 $(m, n)=1$.

欧拉函数$\phi(n)$在第2.8节的练习23中为正整数$n$定义如下:$\phi(n)$是正整数的个数$m$,使得$1 \leq m \leq n$和$(m, n)=1$。由定理3.21和3.28可知,阶为$n$的循环群$\langle a\rangle$有$\phi(n)$个不同的生成器。

例9设$G=\langle a\rangle$为10阶的环群。小于10且相对质数为10的正整数为$1,3,7$和9。因此,列表中包含$G$的所有生成器
$a, a^3, a^7$和$a^9$, $G$有$\phi(10)=4$个不同的生成器。

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