Linear representations and Maschke decomposition
Research context
postgraduate concept · established · As of 2026-10-10
A representation of a finite group G is a homomorphism G→GL(V).
Key knowledge
A representation of a finite group G is a homomorphism G→GL(V). If the field characteristic does not divide |G|, every invariant subspace in a finite-dimensional representation has an invariant complement: average an arbitrary projection over the group. In characteristic p dividing |G| this averaging denominator is unavailable and complete reducibility can fail.
Values and equations
P_G=(1/|G|) sum_g rho(g) P rho(g)^(-1)
- rho
- Representation of a finite group
- P
- Any projection onto an invariant subspace
- P_G
- Averaged invariant projection
Conditions and scope
- V is finite-dimensional over the specified field; |G| is invertible in that field.
- Irreducibility over R and over C are different questions; scalar extension can change the decomposition.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Author checked this English statement, displayed equation where present and stated hypotheses against these source locations: Chapter 7, matrix representations pp. 101–103, Maschke pp. 103–105, characters pp. 115–119. The check is bounded to the recorded claims; no complete proof reconstruction, software proof replay or universal literature completeness is claimed.
2026-10-10 · Author source-body/statement/equation/domain check, with graph associations scoped individually. Separate independent content/source/inventory review is required before branch closure.
Entry details
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