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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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