In the need of computational tools for epsilon-multiplicity, we provide a criterion for a module with a rank E inside a free module F to have rational epsilon-multiplicity in terms of the finite generation of the saturation Rees algebra of E. In this case, the multiplicity can be related to a Hilbert multiplicity of certain graded algebra. A particular example of this situation is provided: it is shown that the epsilon-multiplicity of monomial modules is Noetherian. Numerical evidence is provided that leads to a conjecture formula for the epsilon-multiplicity of certain monomial curves in the 3-affine space.

<p>Let S be a polynomial ring K[x1,...,xn] over a field K and let F be a non-negatively graded free module over S generated by m basis elements. In this thesis, we study four kinds of upper bounds: degree bounds for Gröbner bases of submodules of F, bounds for arithmetic degrees of S-ideals, regularity bounds for radicals of S-ideals, and Stillman bounds. </p> <p><br></p> <p>Let M be a submodule of F generated by elements with degrees bounded above by D and dim(F/M)=r. We prove that if M is graded, the degree of the reduced Gröbner basis of M for any term order is bounded above by 2[1/2((Dm)^{n-r}m+D)]^{2^{r-1}}. If M is not graded, the bound is 2[1/2((Dm)^{(n-r)^2}m+D)]^{2^{r}}. This is a generalization of bounds for ideals in a polynomial ring due to Dubé (1990) and Mayr-Ritscher (2013).</p> <p><br></p> <p>Our next results are concerned with a homogeneous ideal I in S generated by forms of degree at most d with dim(S/I)=r. In Chapter 4, we show how to derive from a result of Hoa (2008) an upper bound for the regularity of sqrt{I}, which denotes the radical of I. More specifically we show that reg(sqrt{I})<= d^{(n-1)2^{r-1}}. In Chapter 5, we show that the i-th arithmetic degree of I is bounded above by 2*d^{2^{n-i-1}}. This is done by proving upper bounds for arithmetic degrees of strongly stable ideals and ideals of Borel type.</p> <p><br></p> <p>In the last chapter, we explain our progress in attempting to make Stillman bounds explicit. Ananyan and Hochster (2020) were the first to show the existence of Stillman bounds. Together with G. Caviglia, we observe that a possible way of making their results explicit is to find an effective bound for an invariant called D(k,d) and supplement it into their proof. Although we are able to obtain this bound D(k,d) and realize Stillman bounds via an algorithm, it turns out that the computational complexity of Ananyan and Hochster's inductive proof would make the bounds too large to be meaningful. We explain the bad behavior of these Stillman bounds by giving estimates up to degree 3.</p>

<p>The goal of this dissertation is to broaden the classes of ideals for which the generators of residual intersections are known. This is split into two main parts.</p> <p>The first part is Chapter 5, where we prove that, for an ideal I in a local Cohen-Macaulay ring R, under suitable technical assumptions, we are able to express s-residual intersections, for s ≥ μ(I) − 2, in terms of (μ(I) − 2)-residual intersections. This result implies that s- residual intersections can be expressed in terms of links, if μ(I) ≤ ht(I) + 3 and some other hypotheses are satisfied. In Chapter 5, we prove our result using two different methods and two different sets of technical assumptions on the depth conditions satisfied by the ideal I. For Section 5.2 and Section 5.3 we use the properties of Fitting ideals and methods developed in [33] to prove our main result. In these sections, we require I to satisfy the Gs condition and be weakly (s − 2)-residually S2. In Section 5.4, we prove analogous results to those in Section 5.2 and Section 5.3 using disguised residual intersections, a notion developed by Bouca and Hassansadeh in [5].</p> <p>The second part is Chapter 6 where we prove that the n-residual intersections of ideals generated by maximal minors of a 2 × n generic matrix for n ≥ 4 are sums of links. To prove this, we require a series of technical results. We begin by proving the main theorem for this chapter in a special case, using the results of Section 6.1 to compute the generators of the relevant links in a our special case, and then using these generators to compute the Gro ̈bner Basis for the sum of links in Section 6.2. The computation of the Gro ̈bner basis, as well as an application of graph theoretic results about binomial edge ideals [17], allow us to show that our main theorem holds in this special case. Lastly, we conclude our proof in Section 6.3, where we show that n-residual intersections of ideals generated by maximal minors of 2 × n generic matrices commute with specialization maps, and use this to show that the generic n-residual intersections of ideals generated by maximal minors of a 2 × n generic matrix for n ≥ 4 are sums of links. This allows us to prove the main theorem of Chapter 6.</p>

As pointed out by I. Moerdijk and G. Reyes in [63], C&#8734-rings have been studied specially for their use in Singularity Theory and in order to construct topos models for Synthetic Differential Geometry. In this work, we follow a complementary trail, deepening our knowledge about them through a more pure bias, making use of Category Theory and accounting them from a logical-categorial viewpoint. We begin by giving a comprehensive systematization of the fundamental facts of the (equational) theory of C&#8734-rings, widespread here and there in the current literature - mostly without proof - which underly the theory of C&#8734-rings. Next we develop some topics of what we call a &#8734Commutative Algebra, expanding some partial results of [66] and [67]. We make a systematic study of von Neumann-regular C&#8734-rings (following [2]) and we present some interesting results about them, together with their (functorial) relationship with Boolean spaces. We study some sheaf theoretic notions on C&#8734-rings, such as &#8734(locally)-ringed spaces and the smooth Zariski site. Finally we describe classifying toposes for the (algebraic) theory of &#8734 rings, the (coherent) theory of local C&#8734-rings and the (algebraic) theory of von Neumann regular C&#8734-rings. / Conforme observado por I. Moerdijk e G. Reyes em [63], os anéis C&#8734 têm sido estudados especialmente tendo em vista suas aplicações em Teoria de Singularidades e para construir toposes que sirvam de modelos para a Geometria Diferencial Sintética. Neste trabalho, seguimos um caminho complementar, aprofundando nosso conhecimento sobre eles por um viés mais puro, fazendo uso da Teoria das Categorias e os analisando a partir de pontos de vista algébrico e lógico-categorial. Iniciamos o trabalho apresentando uma sistematização abrangente dos fatos fundamentais da teoria (equacional) dos anéis C&#8734, distribuídos aqui e ali na literatura atual - a maioria sem demonstrações - mas que servem de base para a teoria. Na sequência, desenvolvemos alguns tópicos do que denominamos Álgebra Comutativa C&#8734, expandindo resultados parciais de [66] e [67]. Realizamos um estudo sistemático dos anéis C&#8734 von Neumann-regulares - na linha do estudo algébrico realizado em [2]- e apresentamos alguns resultados interessantes a seu respeito, juntamente com sua relação (funtorial) com os espaços booleanos. Estudamos algumas noções pertinentes à Teoria de Feixes para anéis &#8734, tais como espaços (localmente) &#8734anelados e o sítio de Zariski liso. Finalmente, descrevemos toposes classicantes para a teoria (algébrica) dos anéis C&#8734, a teoria (coerente) dos anéis locais C&#8734 e a teoria (algébrica) dos anéis C&#8734 von Neumann regulares.

In this dissertation, we consider six Prufer-like conditions on acommutative ring R. These conditions form a hierarchy. Being a Prufer ring is not a local property: a Prufer ring may not remain a Prufer ring when localized at a prime or maximal ideal. We introduce a seventh condition based on this fact and extend the hierarchy. All the conditions of the hierarchy become equivalent in the case of a domain, namely a Prufer domain. We also seek the relationship of the hierarchy with strong Prufer rings. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2015 / FAU Electronic Theses and Dissertations Collection

As pointed out by I. Moerdijk and G. Reyes in [63], C&#8734-rings have been studied specially for their use in Singularity Theory and in order to construct topos models for Synthetic Differential Geometry. In this work, we follow a complementary trail, deepening our knowledge about them through a more pure bias, making use of Category Theory and accounting them from a logical-categorial viewpoint. We begin by giving a comprehensive systematization of the fundamental facts of the (equational) theory of C&#8734-rings, widespread here and there in the current literature - mostly without proof - which underly the theory of C&#8734-rings. Next we develop some topics of what we call a &#8734Commutative Algebra, expanding some partial results of [66] and [67]. We make a systematic study of von Neumann-regular C&#8734-rings (following [2]) and we present some interesting results about them, together with their (functorial) relationship with Boolean spaces. We study some sheaf theoretic notions on C&#8734-rings, such as &#8734(locally)-ringed spaces and the smooth Zariski site. Finally we describe classifying toposes for the (algebraic) theory of &#8734 rings, the (coherent) theory of local C&#8734-rings and the (algebraic) theory of von Neumann regular C&#8734-rings. / Conforme observado por I. Moerdijk e G. Reyes em [63], os anéis C&#8734 têm sido estudados especialmente tendo em vista suas aplicações em Teoria de Singularidades e para construir toposes que sirvam de modelos para a Geometria Diferencial Sintética. Neste trabalho, seguimos um caminho complementar, aprofundando nosso conhecimento sobre eles por um viés mais puro, fazendo uso da Teoria das Categorias e os analisando a partir de pontos de vista algébrico e lógico-categorial. Iniciamos o trabalho apresentando uma sistematização abrangente dos fatos fundamentais da teoria (equacional) dos anéis C&#8734, distribuídos aqui e ali na literatura atual - a maioria sem demonstrações - mas que servem de base para a teoria. Na sequência, desenvolvemos alguns tópicos do que denominamos Álgebra Comutativa C&#8734, expandindo resultados parciais de [66] e [67]. Realizamos um estudo sistemático dos anéis C&#8734 von Neumann-regulares - na linha do estudo algébrico realizado em [2]- e apresentamos alguns resultados interessantes a seu respeito, juntamente com sua relação (funtorial) com os espaços booleanos. Estudamos algumas noções pertinentes à Teoria de Feixes para anéis &#8734, tais como espaços (localmente) &#8734anelados e o sítio de Zariski liso. Finalmente, descrevemos toposes classicantes para a teoria (algébrica) dos anéis C&#8734, a teoria (coerente) dos anéis locais C&#8734 e a teoria (algébrica) dos anéis C&#8734 von Neumann regulares.

L'objet de cette thèse est une description effective des espaces de modules des courbes hyper- elliptiques de genre 3 en caractéristiques positives. En caractéristique nulle ou impaire, on obtient une paramétrisation de ces espaces de modules par l'intermédiaire des algèbres d'invariants pour l'action du groupe spécial linéaire sur les espaces de formes binaires de degré 8, qui sont de type fini. Suite aux travaux de Lercier et Ritzenthaler, les cas des corps de caractéristiques 3, 5 et 7 restaient ouverts. Pour ces derniers, les méthodes classiques de la caractéristique nulle sont inno- pérantes pour l'obtention de générateurs pour les algèbres d'invariants en jeu. Nous nous sommes donc contenté d'exhiber des invariants séparants en caractéristiques 3 et 7. En outre, nos résultats concernant la caractéristique 5 suggèrent l'inadéquation de cette approche pour ce cas. À partir de ces résultats, nous avons pu expliciter la stratification des espaces de modules des courbes hyperelliptiques de genre 3 en caractéristiques 3 et 7 selon les groupes d'automorphismes et implémenté divers algorithmes, dont celui de Mestre, pour la reconstruction d'une courbe à partir de son module, ie la valeur de ses invariants. Pour cette phase de reconstruction, nous nous sommes notamment attaché aux questions arithmétiques, comme l'existence d'une obstruction à être un corps de définition pour le corps de module et, dans le cas contraire, à l'obtention d'un modèle de la courbe sur ce corps minimal. Enfin pour la caractéristique 2, notre approche est différente, dans la mesure où les courbes sont étudiées via leur modèle d'Artin-Schreier. Nous exhibons pour celles-ci des invariants bigradués qui dépendent de la structure arithmétique des points de ramifications des courbes. / The aim of this thesis is to provide an explicite description of the moduli spaces of genus 3 hyperelliptic curves in positive characteristic. Over a field of characteristic zero or odd, a parame- terization of these moduli spaces is given via the algebra of invariants of binary forms of degree 8 under the action of the special linear group. After the work of Lercier and Ritzenthaler, the case of fields of characteristic 3, 5 and 7 are still open. However, in these remaining case, the classical methods in characteristic zero do not work in order to provide generators for these algebra of invariants. Hence we provide only separating invariants in characteristic 3 and 7. Furthermore our results in characteristic 5 show this approach is not suitable. From these results, we describe the stratification of the moduli spaces of genus 3 hyperelliptic curves in characteristic 3 and 7 according to the automorphism groups of the curves and imple- ment algorithms to reconstruct a curve from its invariants. For this reconstruction stage, we paid attention to arithmetic issues, like the obstruction to be a field of definition for the field of moduli. Finally, in the characteristic 2 case, we use a different approach, given that the curves are defined by their Artin-Schreier models. The arithmetic structure of the ramification points of these curves stratify the moduli space in 5 cases and we define in each case invariants that characterize the isomorphism class of hyperelliptic curves.

<div>Let A be a d by n integer matrix. Gel'fand et al.\ proved that most A-hypergeometric systems have an interpretation as a Fourier–Laplace transform of a direct image. The set of parameters for which this happens was later identified by Schulze and Walther as the set of not strongly resonant parameters of A. A similar statement relating A-hypergeometric systems to exceptional direct images was proved by Reichelt. In the first part of this thesis, we consider a hybrid approach involving neighborhoods U of the torus of A and consider compositions of direct and exceptional direct images. Our main results characterize for which parameters the associated A-hypergeometric system is the inverse Fourier–Laplace transform of such a "mixed Gauss–Manin system". </div><div><br></div><div>If the semigroup ring of A is normal, we show that every A-hypergeometric system is "mixed Gauss–Manin". </div><div><br></div><div>In the second part of this thesis, we use our notion of mixed Gauss–Manin systems to show that the projection and restriction of a normal A-hypergeometric system to the coordinate subspace corresponding to a face are isomorphic up to cohomological shift; moreover, they are essentially hypergeometric. We also show that, if A is in addition homogeneous, the holonomic dual of an A-hypergeometric system is itself A-hypergeometric. This extends a result of Uli Walther, proving a conjecture of Nobuki Takayama in the normal homogeneous case.</div>

In this thesis, we undertake a combinatorial study of certain aspects of triangulations of cartesian products of simplices, particularly in relation to their relevance in toric algebra and to their underlying product structure. The first chapter reports joint work with Samu Potka. The object of study is a class of homogeneous toric ideals called cut ideals of graphs, that were introduced by Sturmfels and Sullivant 2006. Apart from their inherent appeal to combinatorial commutative algebra, these ideals also generalize graph statistical models for binary data and are related to some statistical models for phylogenetic trees. Specifically, we consider minimal free resolutions for the cut ideals of trees. We propose a method to combinatorially estimate the Betti numbers of the ideals in this class. Using this method, we derive upper bounds for some of the Betti numbers, given by formulas exponential in the number of vertices of the tree. Our method is based on a common technique in commutative algebra whereby arbitrary homogeneous ideals are deformed to initial monomial ideals, which are easier to analyze while conserving some of the information of the original ideals. The cut ideal of a tree on n vertices turns out to be isomorphic to the Segre product of the cut ideals of its n-1 edges (in particular, its algebraic properties do not depend on its shape). We exploit this product structure to deform the cut ideal of a tree to an initial monomial ideal with a simple combinatorial description: it coincides with the edge ideal of the incomparability graph of the power set of the edges of the tree. The vertices of the incomparability graph are subsets of the edges of the tree, and two subsets form an edge whenever they are incomparable. In order to obtain algebraic information about these edge ideals, we apply an idea introduced by Dochtermann and Engström in 2009 that consists in regarding the edge ideal of a graph as the (monomial) Stanley-Reisner ideal of the independence complex of the graph. Using Hochster\''s formula for computting Betti numbers of Stanley-Reisner ideals by means of simplicial homology, the computation of the Betti numbers of these monomial ideals is turned to the enumeration of induced subgraphs of the incomparability graph. That the resulting values give upper bounds for the Betti numbers of the cut ideals of trees is an important well-known result in commutative algebra. In the second chapter, we focus on some combinatorial features of triangulations of the point configuration obtained as the cartesian product of two standard simplices. These were explored in collaboration with César Ceballos and Arnau Padrol, and had a two-fold motivation. On the one hand, we intended to understand the influence of the product structure on the set of triangulations of the cartesian product of two point configurations; on the other hand, the set of all triangulations of the product of two simplices is an intricate and interesting object that has attracted attention both in discrete geometry and in other fields of mathematics such as commutative algebra, algebraic geometry, enumerative geometry or tropical geometry. Our approach to both objectives is to examine the circumstances under which a triangulation of the polyhedral complex given by the the product of an (n-1)-simplex times the (k-1)-skeleton of a (d-1)-simplex extends to a triangulation of an (n-1)-simplex times a (d-1)-simplex. We refer to the former as a partial triangulation of the product of two simplices. Our main result says that if d >= k > n, a partial triangulation always extends to a uniquely determined triangulation of the product of two simplices. A somewhat unexpected interpretation of this result is as a finiteness statement: it asserts that if d is sufficiently larger than n, then all partial triangulations are uniquely determined by the (compatible) triangulations of its faces of the form “(n-1)-simplex times n-simplex”. Consequently, one can say that in this situation ‘\''triangulations of an (n-1)-simplex times a (d-1)-simplex are not much more complicated than triangulations of an (n-1)-simplex times an n-simplex\''\''. The uniqueness assertion of our main result holds already when d>=k>=n. However, the same is not true for the existence assertion; namely, there are non extendable triangulations of an (n-1)-simplex times the boundary of an n-simplex that we explicitly construct. A key ingredient towards this construction is a triangulation of the product of two (n-1)-simplices that can be seen as its ``second simplest triangulation\''\'' (the simplest being its staircase triangulation). It seems to be knew, and we call it the Dyck path triangulation. This triangulation displays symmetry under the cyclic group of order n that acts by simultaneously cycling the indices of the points in both factors of the product. Next, we exhibit a natural extension of the Dyck path triangulation to a triangulation of an (n-1)-simplex times an n-simplex that, in a sense, enjoys some sort of ‘\''rigidity\''\'' (it also seems new). Performing a ‘\''local modification\''\'' on the restriction of this extended triangulation to the polyhedral complex given by (n-1)-simplex times the boundary of an n-simplex yields the non-extendable partial triangulation. The thesis includes two appendices on basic commutative algebra and triangulations of point configuration, included to make it slightly self-contained.

In his study of spectra of f-rings via pointfree topology, Banaschewski [6] considers lattices of l-ideals, radical l-ideals, and saturated l-ideals of a given f-ring A. In each case he shows that the lattice of each of these kinds of ideals is a coherent frame. This means that it is compact, generated by its compact elements, and the meet of any two compact elements is compact. This will form the basis of our main goal to show that the lattice-ordered rings studied in [6] are coherent frames. We conclude the dissertation by revisiting the d-elements of Mart nez and Zenk [30], and characterise them analogously to d-ideals in commutative rings. We extend these characterisa-tions to algebraic frames with FIP. Of necessity, this will require that we reappraise a great deal of Banaschewski's work on pointfree spectra, and that of Mart nez and Zenk on algebraic frames. / Mathematical Sciences / M. Sc. (Mathematics)