Auslander regular algebras and Coxeter matrices

TL;DR

This paper establishes a linear algebraic interpretation of the grade bijection for Auslander regular algebras, linking it to Coxeter matrices and providing new computational and theoretical insights.

Contribution

It demonstrates that the grade bijection coincides with the permutation matrix in the Coxeter matrix's Bruhat factorization, offering a new linear algebraic perspective and applications.

Findings

The permanent of the Coxeter matrix is ±1.

Distributive lattices characterized by Coxeter matrices as PU.

New homological results for modules in category O.

Abstract

We show that Iyama's grade bijection for Auslander-Gorenstein algebras coincides with the bijection introduced by Auslander-Reiten. This result uses a new characterisation of Auslander-Gorenstein algebras. Furthermore, we show that the grade bijection of an Auslander regular algebra coincides with the permutation matrix P in the Bruhat factorisation of the Coxeter matrix. This gives a new, purely linear algebraic interpretation of the grade bijection and allows us to calculate it in a much quicker way than was previously known. We give several applications of our main results. First, we show that the permanent of the Coxeter matrix of an Auslander regular algebra is either 1 or -1. Second, we obtain a new combinatorial characterisation of distributive lattices among the class of finite lattices. Explicitly, a lattice is distributive if and only if its Coxeter matrix can be written as PU where P is a permutation matrix and U is an upper triangular matrix. Other applications include new homological results about modules in blocks of category $\mathcal{O}$ of semisimple Lie algebras.