Anyone recognize this subgroup?

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Homework Help Overview

The discussion revolves around the subgroup defined in the context of permutation groups, specifically focusing on the set of permutations that leave a particular element unchanged. Participants are exploring the implications and characteristics of this subgroup, denoted as G_a.

Discussion Character

  • Conceptual clarification, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are attempting to understand the nature of the subgroup G_a, with some questioning whether it is simply the identity group. Others are exploring the concept of group actions and how they relate to this subgroup. There are discussions about specific examples of permutations and their effects on the set.

Discussion Status

The discussion is active, with participants sharing their interpretations and seeking clarification on the subgroup's properties. Some have provided examples to illustrate their points, while others express confusion and seek further insights into the concept of actions in relation to the subgroup.

Contextual Notes

Participants mention a lack of familiarity with the concept of group actions, indicating that this discussion is occurring in a learning context where foundational knowledge may be incomplete. There is also a reference to a geometry class, suggesting that the topic may be new to some participants.

Juanriq
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Ahoy hoy, let A be a set with a \in A. Define

G_a = \{ g \in S_A; g(a) = a \}

Where S_A is the permutation group. Are we just talking the set of all inverses of the permutation group? Thanks!
 
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isn't it the set which leaves a unchanged in a permutation?
 
Have you seen the concept of "actions" yet?
 
Hey guys, I think I don't understand what this subgroup does. Lanedance, I think I see what you mean, but wouldn't that just be like an identity group? I don't understand what would be so special about some group that just spits the same thing back out all the time... Also, micromass, I have not seen actions yet. This came up in a geometry class after we spent 5 minutes on the permutation group. I understand what the permutation group is, but this subgroup really means nothing to me. Any enlightening ideas would be welcome, I'm going to go wikipedia actions.
 
Juanriq said:
Hey guys, I think I don't understand what this subgroup does. Lanedance, I think I see what you mean, but wouldn't that just be like an identity group? I don't understand what would be so special about some group that just spits the same thing back out all the time...

as i read it, it only has to leave the element a unchanged
 
so if a=(321), then g(321) = (321), right?
 
the inverse of G_a is the identity?
 
i would have thought it was somthing like
A = {a,b,c}

the set of all permutations of A is S_A
{a,b,c} ()
{b,a,c} (12)
{c,b,a} (13)
{a,c,b} (23)
{b,c,a} (123)

the set of all permutations that leave a unchanged are S_a
{a,b,c} ()
{a,c,b} (23)
 
Ohhhhh... that's something completely different than what I was thinking. Thanks lanedance!
 

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