# When is a polynomial ideal binomial after an ambient automorphism?

## TL;DR

This paper develops algorithms to determine when polynomial ideals can be transformed into binomial or toric forms via coordinate changes, with applications to algebraic geometry and computational algebra.

## Contribution

It introduces new probabilistic and deterministic algorithms for identifying binomial and toric structures in polynomial ideals under coordinate transformations.

## Key findings

- Algorithms effectively find loci where ideals are binomial or unital binomial.
- Probabilistic algorithms are faster than existing deterministic methods.
- Applications include classifying toric varieties and stabilizer subgroups in algebraic group actions.

## Abstract

Can an ideal I in a polynomial ring k[x] over a field be moved by a change of coordinates into a position where it is generated by binomials $x^a - cx^b$ with c in k, or by unital binomials (i.e., with c = 0 or 1)? Can a variety be moved into a position where it is toric? By fibering the G-translates of I over an algebraic group G acting on affine space, these problems are special cases of questions about a family F of ideals over an arbitrary base B. The main results in this general setting are algorithms to find the locus of points in B over which the fiber of F - is contained in the fiber of a second family F' of ideals over B; - defines a variety of dimension at least d; - is generated by binomials; or - is generated by unital binomials. A faster containment algorithm is also presented when the fibers of F are prime. The big-fiber algorithm is probabilistic but likely faster than known deterministic ones. Applications include the setting where a second group T acts on affine space, in addition to G, in which case algorithms compute the set of G-translates of I - whose stabilizer subgroups in T have maximal dimension; or - that admit a faithful multigrading by $Z^r$ of maximal rank r. Even with no ambient group action given, the final application is an algorithm to - decide whether a normal projective variety is abstractly toric. All of these loci in B and subsets of G are constructible; in some cases they are closed.