Why Does the Field Choice Affect Maschke's Theorem Application to Group C2?

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SUMMARY

Maschke's theorem states that for a finite group G, the field F must not have a characteristic that divides the order of G for the theorem to apply. Specifically, for the cyclic group C2, the field F cannot be F2, as 2 is not invertible in F2. The theorem's validity hinges on the ability to multiply by the multiplicative inverse of |G| in the chosen field. Therefore, the relationship between the group size and the field's characteristics is critical for the application of Maschke's theorem.

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  • Understanding of finite groups, specifically cyclic groups like C2.
  • Knowledge of field theory, particularly field characteristics and invertibility.
  • Familiarity with Maschke's theorem and its implications in representation theory.
  • Basic concepts of group order and its relation to field elements.
NEXT STEPS
  • Study the implications of field characteristics on group representations.
  • Learn about the multiplicative inverse in various fields, focusing on F2.
  • Explore advanced topics in representation theory, particularly the applications of Maschke's theorem.
  • Investigate the relationship between group order and field characteristics in more complex groups.
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Mathematicians, particularly those specializing in group theory and representation theory, as well as students seeking to understand the implications of field choices in the application of Maschke's theorem.

catcherintherye
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In the statement of Maschke's theroem we are told 'Let G be a finite group and F a field in which |G| not equal to zero. As an example we are told if our group was C2 (cyclic) then we could not have F=F2 (the field with 2 elements). I fail to see how C2 and F2 are related, surely |C2|=2 regardless of F. I do not see how changing the field changes the size of the group. What am I missing??
 
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It doesn't alter the size of the group. Nothing says that choosing the field changes the size of the group - I don't see where you got that conclusion from.

|C_2| is certainly 2, and Maschke's result holds in any field where 2 is invertible (i.e. precisely not F_2 or any extension).

Maschke's theorem, or its proof, requires that one is able to multiply through by the multiplicative inverse of |G| in F.
 
All the versions of Maschke's theorem that I am familiar with say "over a field of characteristic k where k does not divide |G|" or the equivalent "Over a field in which |G| is not a zero divisor". If your text actually says "over a field in which |G| not equal to zero"- that is very sloppy language.
 

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