**SMS scnews item created by Boris Lishak at Mon 16 Sep 2019 1601**

Type: Seminar

Distribution: World

**Calendar1: 23 Sep 2019 1200-1300**

**CalLoc1: Carslaw 375**

CalTitle1: Helmer -- Segre-Driven Containment Testing for Varieties

Auth: borisl@dora.maths.usyd.edu.au

### Geometry and Topology Seminar

# Segre-Driven Containment Testing for Varieties

### Martin Helmer (ANU)

September 23, 12:00-13:00 in Carslaw 375
Seminar schedule

Please join us for lunch after the talk.

**Abstract:**
In this talk we consider new methods to test pairwise containment of projective vareities (i.e. the solutions to systems of homogenous polynomial equations). Previous aproaches to this problem have doubly exponetial complexity, in this talk we present a new effective algorithm with singly exponetial complexity. More generally this algorithm can test pairwise containment of arbitrary (possibly singular) subvarieties of any smooth projective toric variety and can also determine algebraic multiplicity without working in local rings. These methods may be implemented without using GrÃ¶bner bases; in particular numeric methods can be used. The methods arise from techniques developed to compute the Segre class s(X,Y) of X in Y for X and Y arbitrary subschemes of some smooth projective toric variety T. In particular, this work also gives an explicit method to compute these Segre classes and other associated objects such as the Fulton-MacPherson intersection product of projective varieties (this intersection product captures the behavior of intersections of two varieites inside a third). These algorithms are implemented in Macaulay2 and have been found to be effective on a variety of examples. This is joint work with Corey Harris (University of Oslo).