[Math] Dihedral Group of Order 12 in Cycle Notation

abstract-algebracombinatoricsdihedral-groupsgeometrygroup-theory

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I want to check that this cycle notation is correct for the Dihedral Group of order $12$. I found this graph in Wikipedia. I did not find the cycle notation. May you please tell me if my cycle notation is correct?

Here is my solution: I will name the vertices $1,2,3,4,5,6$ in the clockwise direction.

1) Rotation 0 degrees

$(1)(2)(3)(4)(5)(6)$

2) Rotation 60 degrees (clockwise direction)

$(123456)$

3) Rotation 120 degrees

$(135)(246)$

4) Rotation 180 degrees

$(14)(25)(36)$

5) Rotation 240 degrees

$(153)(264)$

6) Rotation 300 degrees

$(165432)$

7) Flip 2-5

$(2)(5)(13)(46)$

8) Flip 1-4

$(1)(4)(26)(35)$

9) Flip 3-6

$(3)(6)(15)(24)$

10) Flip A

$(12)(36)(45)$

11) Flip B

$(14)(23)(56)$

12) Flip C

$(16)(25)(34)$

Best Answer

There is a computationally easier way to do this, and you do not even need to revisit the geometric intepretation of $\operatorname{Dih}(6)$. Let $\phi:\operatorname{Dih}(6)\times\{1,2,3,4,5,6\}\rightarrow\{1,2,3,4,5,6\}$ be the group action of the dihedral group of a regular hexagon on the six vertices. Let $\varphi:\operatorname{Dih}(6)\rightarrow\operatorname{Sym}(6)$ be the permutation representation afforded by the action. Then write $\varphi(r)=(123456)$ and $\varphi(s)=(13)(46)$. Then since $\varphi$ is a homomorphism, and $\operatorname{Dih}(6)=\{1,r,r^2,\dots,s,sr,sr^2\dots\}$ is generated by $r$ and $s$, you can compute the cycle representation of each element of $\operatorname{Dih}(6)$, e.g. $\varphi(sr^2)=\varphi(s)\varphi(r)^2=(13)(46)(123456)^2=\dots$ (check it yourself :D).

P.S. Hmm... it seems that your answer is correct, but you should check it again using the group action approach anyway.

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