Linearly presented perfect ideals of codimension $2$ in three variables

TL;DR

This paper investigates the detailed structure of linearly presented perfect ideals of codimension 2 in three variables, focusing on their Rees algebra, special fiber, and minors of Hilbert--Burch matrices, extending previous work without generic assumptions.

Contribution

It extends the understanding of these ideals by analyzing their minors and conjugation properties, applying results to models like plane fat points, hyperplane arrangements, and monomial ideals.

Findings

Characterization of Rees algebra and special fiber properties.

Extension of Lan's work on non-generic ideals.

Applications to specific geometric and algebraic models.

Abstract

The goal of this paper is the fine structure of the ideals in the title, with emphasis on the properties of the associated Rees algebra and the special fiber. The watershed between the present approach and some of the previous work in the literature is that here one does not assume that the ideals in question satisfy the common generic properties. One exception is a recent work of N. P. H. Lan which inspired the present work. Here we recover and extend his work. We strongly focus on the behavior of the ideals of minors of the corresponding so-called Hilbert--Burch matrix and on conjugation features of the latter. We apply the results to three important models: linearly presented ideals of plane fat points, reciprocal ideals of hyperplane arrangements and linearly presented monomial ideals.