## Segre class computation and practical applications

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Corey Harris and Martin Helmer
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## Abstract:

Let $X \subset Y$ be closed (possibly singular) subschemes of a smooth projective toric variety $T$. We show how to compute the Segre class ${s}(X,Y)$ as a class in the Chow group of $T$. Building on this, we give effective methods to compute intersection products in projective varieties, to determine algebraic multiplicity*without*working in local rings, and to test pairwise containment of subvarieties of $T$. Our methods may be implemented without using Gröbner bases; in particular any algorithm to compute the number of solutions of a zero-dimensional polynomial system may be used.

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## Additional Information

**Corey Harris**- Affiliation: Department of Mathematics, University of Oslo, P.O. Box 1053 Blindern, 0316 Oslo, Norway
- Email: charris@math.uio.no
**Martin Helmer**- Affiliation: Department of Mathematical Sciences, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark
- Address at time of publication: Mathematical Sciences Institute, Hanna Neumann Building, Science Road, The Australian National University, Canberra ACT 2601 Australia
- MR Author ID: 884722
- Email: martin.helmer2@gmail.com
- Received by editor(s): July 13, 2018
- Received by editor(s) in revised form: February 15, 2019
- Published electronically: May 24, 2019
- Additional Notes: The first author was partially supported by the Bergen Research Foundation project grant “Algebraic and topological cycles in tropical and complex geometry”.

The second author was partially supported by the Independent Research Fund of Denmark during the preparation of this work. - © Copyright 2019 American Mathematical Society
- Journal: Math. Comp.
**89**(2020), 465-491 - MSC (2010): Primary 14Qxx, 13Pxx, 13H15, 14C17, 14C20, 68W30, 65H10
- DOI: https://doi.org/10.1090/mcom/3448
- MathSciNet review: 4011552