Re: representing the dihedral group {1,r,r^2...s,sr^2...}

• To: mathgroup at smc.vnet.net
• Subject: [mg98861] Re: representing the dihedral group {1,r,r^2...s,sr^2...}
• From: dh <dh at metrohm.com>
• Date: Mon, 20 Apr 2009 19:09:44 -0400 (EDT)
• References: <gsh100\$gr\$1@smc.vnet.net>

```
Hi,

it calls for troubles changing the rules for built in functions. Instead

assigne the rule to your symbols. E.g.:

s /: s^2 = 1;

s /: s^n_ := s s^(n - 1) /. n > 2;

r /: r^4 = 1;

r /: r^n_ := r r^(n - 1) /; n > 4;

Daniel

obott0 at gmail.com wrote:

> Hi, I'm trying to represent the dihedral group {1,r,r^2...s,sr^2...}

> in mathematica so I can do for example:

>

> s^3

>

> and get s.

>

> I tried this code:

>

> Unprotect[Times, Power];

> n = 4;

> ClearAll[r, s, Times, Power];

> SetAttributes[Times, {Flat}]

> s^2 = 1;

> r^n = 1;

> Protect[Times, Power];

>

> But this doesn't work for, for example, s^3. It is not able to

> simplify it.

>

> Thanks a lot!

>

> Otto

>

```

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