Algebraic Geometry

Minimal Length Maximal Green Sequences and Triangulations of Polygons

Group Members

Emily Cormier, Peter Dillery, Jill ReshJohn WhelanAlgebraic Geometry

Supervisors

Khrystyna Serhiyenko

Overview

Maximal green sequences (MGS’s) are combinatorial objects that involve local transformations of directed graphs, also called quivers.  We studied minimal length MGS’s for quivers of type A.   It is know that such quivers are in bijection with triangulations of polygons.  Moreover, these local transformations of quivers behave well under this correspondence, and there is a related notion of mutation of triangulations.  This enabled us to study MGS’s both in terms of quivers and in terms of triangulations. We showed that any minimal length MGS has length n+t, where n is the number of vertices in the quiver and t is the number of 3-cycles.  We also developed an algorithm that yields such sequences of minimal length.

Presentation

Minimal Length Maximal Green Sequences

Poster

Frobenius Splitting of Projective Toric Varieties

Jed Chou, Ben Whitney

Group Members

Jed Chou and Ben Whitney

Overview

A toric variety is an algebraic variety containing the algebraic torus (C*)n as an open dense subset such that the action of the torus extends to the whole variety. Every n-dimensional toric variety can be associated to a fan, which can be given as a set of primitive vectors in an n-dimensional lattice N. Because of this association, many properties of toric varieties can be studied using combinatorial methods. This group was interested in determining which projective toric varieties are Frobenius split. If a projective toric variety is Frobenius split, it has many nice properties. For example, it can be given as the solution set to homogeneous degree two polynomials.

Sam Payne proved in 2008 that a toric variety is Frobenius split if and only if an associated polytope called the splitting polytope contains representatives of every residue class of (1/q)M/M where M is the dual lattice to N. The group’s goal was to use this characterization of Frobenius splitting to classify the Frobenius split projective toric varieties in n dimensions. Given a trivalent tree where edges are labeled with variables and integers, it’s possible to construct the fan of a toric variety. They determined which toric varieties arising in this way are Frobenius split for certain classes of edge labelings.