English

Algorithmic construction of representations of finite solvable groups

Representation Theory 2018-10-10 v1

Abstract

The dominant theme of this thesis is the construction of matrix representations of finite solvable groups using a suitable system of generators. For a finite solvable group GG of order N=p1p2pnN = p_{1}p_{2}\dots p_{n}, where pip_{i}'s are primes, there always exists a subnormal series: e=Go<G1<<Gn=G\langle {e} \rangle = G_{o} < G_{1} < \dots < G_{n} = G such that Gi/Gi1G_{i}/G_{i-1} is isomorphic to a cyclic group of order pip_{i}, i=1,2,,ni = 1,2,\dots,n. Associated with this series, there exists a system of generators consisting nn elements x1,x2,,xnx_{1}, x_{2}, \dots, x_{n} (say), such that Gi=x1,x2,,xiG_{i} = \langle x_{1}, x_{2}, \dots, x_{i} \rangle, i=1,2,,ni = 1,2,\dots,n, which is called a "long system of generators". In terms of this system of generators and conjugacy class sum of xix_{i} in GiG_{i}, i=1,2,,ni = 1,2, \dots, n, we present an algorithm for constructing the irreducible matrix representations of GG over C\mathbb{C} within the group algebra C[G]\mathbb{C}[G]. This algorithmic construction needs the knowledge of primitive central idempotents, a well defined set of primitive (not necessarily central) idempotents and the "diagonal subalgebra" of C[G]\mathbb{C}[G]. In terms of this system of generators, we give simple expressions for the primitive central idempotents, a well defined system of primitive (not necessarily central) idempotents and a convenient set of generators of the "diagonal subalgebra" of C[G]\mathbb{C}[G]. For a finite abelian group, we present an algorithm for constructing the inequivalent irreducible matrix representations over a field of characteristic 00 or prime to the order of the group and a systematic way of computing the primitive central idempotents of the group algebra. Besides that, we give simple expressions of the primitive central idempotents of the rational group algebra of a finite abelian group using a "long presentation" and it's Wedderburn decomposition.

Keywords

Cite

@article{arxiv.1810.04015,
  title  = {Algorithmic construction of representations of finite solvable groups},
  author = {Soham Swadhin Pradhan},
  journal= {arXiv preprint arXiv:1810.04015},
  year   = {2018}
}

Comments

PhD thesis, Indian Institute of Technology, Bombay (2018)