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 Post subject: Defition of cyclic groups.
PostPosted: Sun, 8 Apr 2012 01:35:24 UTC 
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I'm trying to understand the definition of a cyclic group:
"Cyclic Group: If 'a' is in a group G, and every element of G is a power of 'a' G={a^n : n in Z}, then G is a cyclic group and 'a' is its generator, G=<a>."

What does it mean by "every element of G is a power of 'a' ?" What is a example of this?


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 Post subject: Re: Defition of cyclic groups.
PostPosted: Sun, 8 Apr 2012 05:11:27 UTC 
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DgrayMan wrote:
I'm trying to understand the definition of a cyclic group:
"Cyclic Group: If 'a' is in a group G, and every element of G is a power of 'a' G={a^n : n in Z}, then G is a cyclic group and 'a' is its generator, G=<a>."

What does it mean by "every element of G is a power of 'a' ?" What is a example of this?


For example, take the group of rotations of a regular n-gon. The rotation about centre by \frac{2\pi}{n} is a generator --- every other rotation is a composite of it or its inverse.

_________________
\begin{aligned}
Spin(1)&=O(1)=\mathbb{Z}/2&\quad&\text{and}\\
Spin(2)&=U(1)=SO(2)&&\text{are obvious}\\
Spin(3)&=Sp(1)=SU(2)&&\text{by }q\mapsto(\mathop{\mathrm{Im}}\mathbb{H}\ni p\mapsto qp\bar{q})\\
Spin(4)&=Sp(1)\times Sp(1)&&\text{by }(q_1,q_2)\mapsto(\mathbb{H}\ni p\mapsto q_1p\bar{q_2})\\
Spin(5)&=Sp(2)&&\text{by }\mathbb{HP}^1\cong S^4_{round}\hookrightarrow\mathbb{R}^5\\
Spin(6)&=SU(4)&&\text{by the irrep }\Lambda_+\mathbb{C}^4
\end{aligned}


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 Post subject: Re: Defition of cyclic groups.
PostPosted: Sun, 8 Apr 2012 16:02:34 UTC 
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I get it. i think typing it, actually helped me sound it out. thanks.


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