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Bounding the minimal number of generators of an Azumaya algebra. (arXiv:1810.03710v1 [math.RA])
来源于:arXiv
A paper of U. First & Z. Reichstein proves that if $R$ is a commutative ring
of dimension $d$, then any Azumaya algebra $A$ over $R$ can be generated as an
algebra by $d+2$ elements, by constructing such a generating set, but they do
not prove that this number of generators is required, or even that for an
arbitrarily large $r$ that there exists an Azumaya algebra requiring $r$
generators. In this paper, for any given fixed $n\ge 2$, we produce examples of
a base ring $R$ of dimension $d$ and an Azumaya algebra of degree $n$ over $R$
that requires $r(d,n) = \lfloor \frac{d}{2n-2} \rfloor + 2$ generators. While
$r(d,n) < d+2$ in general, we at least show that there is no uniform upper
bound on the number of generators required for Azumaya algebras. The method of
proof is to consider certain varieties $B^r_n$ that are universal varieties for
degree-$n$ Azumaya algebras equipped with a set of $r$ generators, and
specifically we show that a natural map on Chow group $CH^{(r-1)(n-1)} 查看全文>>