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Linear representations of algebras and groups, Lie theory, associative algebras, multilinear algebra.

10 votes
1 answer
363 views

A Realization Problem for Character Tables

Given an $n\times n$ table of complex numbers, are there known sufficient conditions for the table to be the character table of a finite group? Representation theory gives plenty of necessary conditi …
Jon Cohen's user avatar
  • 1,261
7 votes
2 answers
221 views

Irreducibility of Coxeter graphs as a function of generating sets

Given a Coxeter system $(W, S)$, we can form its Coxeter graph, and say that the system is irreducible if the graph is connected. Now, irreducibility is not solely a function of $W$; it depends also o …
Jon Cohen's user avatar
  • 1,261
9 votes
2 answers
1k views

Character table entries and sums of roots of unity

It is well-known that the entries of the character table of a finite group are sums of roots of unity. Question: Is the converse true? Explicitly, given $z\in \mathbb{Z}[\mu_\infty]$, can I find a f …
Jon Cohen's user avatar
  • 1,261