On the universal Gr\"obner bases of varieties of minimal degree

TL;DR

This paper extends the combinatorial description of Graver bases from rational normal curves to scrolls, providing degree bounds for elements in universal Gr"obner bases of varieties of minimal degree.

Contribution

It generalizes the description of Graver bases to rational normal scrolls and establishes sharp degree bounds for their elements.

Findings

Graver basis for scrolls described via colored partition identities

Sharp degree bounds for Graver basis elements established

Degree bounds for reduced Gr"obner basis elements in projected varieties proven

Abstract

A universal Gr\"obner basis of an ideal is the union of all its reduced Gr\"obner bases. It is contained in the Graver basis, the set of all primitive elements. Obtaining an explicit description of either of these sets, or even a sharp degree bound for their elements, is a nontrivial task. In their '95 paper, Graham, Diaconis and Sturmfels give a nice combinatorial description of the Graver basis for any rational normal curve in terms of primitive partition identities. Their result is extended here to rational normal scrolls. The description of the Graver bases is given in terms of colored partition identities. This leads to a sharp bound on the degree of Graver basis elements, which is always attained by a circuit. Finally, for any variety obtained from a scroll by a sequence of projections to some of the coordinate hyperplanes, the degree of any element in any reduced Gr\"obner basis is bounded by the degree of the variety.