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Doctoral thesis . 2020
License: CC BY SA
https://dx.doi.org/10.25673/35...
Doctoral thesis . 2020
License: CC BY SA
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Symmetry in toric geometry

Authors: Ananiadi, Lamprini;

Symmetry in toric geometry

Abstract

Familien algebraischer Varietäten, die durch Monome parametrisiert sind, tauchen in verschiedenen Bereichen der Mathematik, wie zum Beispiel der Statistik, der kommutativen Algebra oder der Kombinatorik auf. Solche Varietäten nennt man torische Varietäten und ihre Untersuchung bildet das Feld der torischen Geometrie. Die Ideale, die solche Varietäten definieren, sind sogenannte Binomialideale. Die torische Geometrie ist häufig durch ein enges Zusammenspiel zwischen algebraischer und polyedrischer Geometrie geprägt, da sich strukturelle Aussagen über eine torische Varietät meist kombinatorisch interpretieren lassen. Ziel dieser Arbeit ist es, Fortschritte in zwei verschiedenen Bereichen an diesem Schnittpunkt zweier Felder zu machen. Im ersten Teil dieser Arbeit, in Kapitel 2 und Kapitel 3, untersuchen wir kombinatorische Objekte im Bereich der torischen Geometrie modulo Symmetrie. Genauer gesagt betrachten wir die korrespondierenden Kegel von Familien von Binomialidealen, deren Anzahl an Variablen unbeschränkt ist, die sich aber modulo Symmetrie stabilisieren. Mit Stabilisierung modulo Symmetrie ist gemeint, dass diese Ideale von den Orbits einer Wirkung der unendlichen symmetrischen Gruppe auf endlich vielen Polynomen erzeugt sind. In Kapitel 2 berechnen wir explizit die Gleichungen und Ungleichungen, die die Facetten der genannten Kegel definieren. Anhand dieser Berechnungen zeigen wir die sogenannte kombinatorische Stabilisierung bestimmter Familien von Kegeln. In Kapitel 3 formulieren wir Kriterien für die Stabilisierung modulo Symmetrie für allgemeine Familien polyedrischer Kegel. Hier ist das zentrale Resultat die Aussage, dass die Stabilisierung einer Familie polyedrischer Kegel modulo Symmetrie die Stabilisierung der korrespondierenden Familie von Monoiden impliziert. Der zweite Teil dieser Arbeit, Kapitel 4, beschäftigt sich mit der Ermittlung der Erzeuger von Idealen, die eine wichtige Rolle bei der Betrachtung spezieller statistischer Modelle, sogenannter Staged Trees, spielen. Unser Hauptresultat bezieht sich auf den Fall, in dem diese Ideale von Binomen erzeugt sind und besagt, dass in diesem Falle die Erzeuger eine quadratische Gröbnerbasis bilden und die Initialideale quadratfrei sind. Dies impliziert, dass für das Polytop der korrespondierenden torischen Varietät eine unimodulare Triangulierung existiert.

Families of algebraic varieties that are parametrized by monomials appear in various areas of mathematics, such as statistics, commutative algebra and combinatorics. Such varieties are referred to as toric varieties and they are the structural objects of toric geometry. The ideals defining toric varieties are prime binomial ideals. Toric geometry is a field of rich interaction between algebraic and polyhedral geometry. We can take statements from algebraic geometry and look for their combinatorial interpretation and vice versa. The main contributions of this thesis are divided in two parts and aim at making progress in two special topics in this intersection. The first part of the thesis, Chapter 2 and Chapter 3, investigates the combinatorial objects arising in toric geometry up to symmetry. Such objects are cones emerging from families of binomial ideals in an increasing number of variables that stabilize up to symmetry, that is, they are generated by the orbit under the action of the infinite symmetric group on finite sets of polynomials. In Chapter 2, we explicitly compute the facets of these cones by providing the description of their defining inequalities and equations. Based on this, we are able to deduce the combinatorial stabilization of the families of cones of our interest. Afterwards, in Chapter 3, we formulate criteria for stabilization up to symmetry for any family of polyhedral cones by looking at families of monoids. The main outcome here is that when a family of cones stabilizes up to symmetry then also the underlying family of monoids stabilizes. The second part of this thesis, Chapter 4, addresses the problem of implicitly computing generating sets of the ideals defining combinatorial objects from statistics called staged trees. The main result states that when a staged tree is defined by a toric ideal, then this ideal is generated by a quadratic Gröbner basis and has squarefree initial ideal. As a consequence, the polytope corresponding to this toric variety has a unimodular triangulation.

Keywords

ddc:510, ddc:511, 511.6, 500, 511, Algebraische Geometrie, 510

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selected citations
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This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
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popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
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