11. Dimension
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Injective Modules: Preparatory Material for the Snowbird Summer School on Commutative Algebra
INJECTIVE MODULES: PREPARATORY MATERIAL FOR THE SNOWBIRD SUMMER SCHOOL ON COMMUTATIVE ALGEBRA These notes are intended to give the reader an idea what injective modules are, where they show up, and, to a small extent, what one can do with them. Let R be a commutative Noetherian ring with an identity element. An R- module E is injective if HomR( ;E) is an exact functor. The main messages of these notes are − Every R-module M has an injective hull or injective envelope, de- • noted by ER(M), which is an injective module containing M, and has the property that any injective module containing M contains an isomorphic copy of ER(M). A nonzero injective module is indecomposable if it is not the direct • sum of nonzero injective modules. Every injective R-module is a direct sum of indecomposable injective R-modules. Indecomposable injective R-modules are in bijective correspondence • with the prime ideals of R; in fact every indecomposable injective R-module is isomorphic to an injective hull ER(R=p), for some prime ideal p of R. The number of isomorphic copies of ER(R=p) occurring in any direct • sum decomposition of a given injective module into indecomposable injectives is independent of the decomposition. Let (R; m) be a complete local ring and E = ER(R=m) be the injec- • tive hull of the residue field of R. The functor ( )_ = HomR( ;E) has the following properties, known as Matlis duality− : − (1) If M is an R-module which is Noetherian or Artinian, then M __ ∼= M. -
Dimension Theory and Systems of Parameters
Dimension theory and systems of parameters Krull's principal ideal theorem Our next objective is to study dimension theory in Noetherian rings. There was initially amazement that the results that follow hold in an arbitrary Noetherian ring. Theorem (Krull's principal ideal theorem). Let R be a Noetherian ring, x 2 R, and P a minimal prime of xR. Then the height of P ≤ 1. Before giving the proof, we want to state a consequence that appears much more general. The following result is also frequently referred to as Krull's principal ideal theorem, even though no principal ideals are present. But the heart of the proof is the case n = 1, which is the principal ideal theorem. This result is sometimes called Krull's height theorem. It follows by induction from the principal ideal theorem, although the induction is not quite straightforward, and the converse also needs a result on prime avoidance. Theorem (Krull's principal ideal theorem, strong version, alias Krull's height theorem). Let R be a Noetherian ring and P a minimal prime ideal of an ideal generated by n elements. Then the height of P is at most n. Conversely, if P has height n then it is a minimal prime of an ideal generated by n elements. That is, the height of a prime P is the same as the least number of generators of an ideal I ⊆ P of which P is a minimal prime. In particular, the height of every prime ideal P is at most the number of generators of P , and is therefore finite. -
On Gelfand-Kirillov Transcendence Degree
TRANSACTIONS OF THE AMERICAN MATHEMATICAL SOCIETY Volume 348, Number 7, July 1996 ON GELFAND-KIRILLOV TRANSCENDENCE DEGREE JAMES J. ZHANG Abstract. We study some basic properties of the Gelfand-Kirillov transcen- dence degree and compute the transcendence degree of various infinite-dimen- sional division algebras including quotient division algebras of quantized alge- bras related to quantum groups, 3-dimensional Artin-Schelter regular algebras and the 4-dimensional Sklyanin algebra. 1. Introduction The Gelfand-Kirillov transcendence degree was introduced in [GK] by I. M. Gelfand and A. A. Kirillov in order to show that the n-th and m-th Weyl divi- sion algebras Dn and Dm are not isomorphic if n = m. For an algebra A over a base field k, the Gelfand-Kirillov transcendence degree6 of A is defined to be n Tdeg(A)=supinf lim logn dim((k + bV ) ) b n V →∞ where V ranges over the subframes (i.e. finite dimensional subspaces containing 1) of A and b ranges over the regular elements of A. The dimension of a k-vector space is always denoted by dim. The Gelfand-Kirillov dimension of A,whichwas also introduced in [GK], is defined to be GKdim(A)=sup lim log dim(V n) n n V →∞ where V ranges over the subframes of A. Gelfand and Kirillov proved that GKdim and Tdeg of the n-th Weyl algebra An are 2n and that Tdeg of the quotient division algebra Dn of An is 2n. On the other hand, L. Makar-Limanov showed that the first Weyl division algebra D1 (and hence Dn for all n 1) contains a noncommutative free subalgebra of two ≥ variables [M-L]. -
The Hermite–Lindemann–Weierstraß Transcendence Theorem
The Hermite–Lindemann–Weierstraß Transcendence Theorem Manuel Eberl March 12, 2021 Abstract This article provides a formalisation of the Hermite–Lindemann– Weierstraß Theorem (also known as simply Hermite–Lindemann or Lindemann–Weierstraß). This theorem is one of the crowning achieve- ments of 19th century number theory. The theorem states that if α1; : : : ; αn 2 C are algebraic numbers that are linearly independent over Z, then eα1 ; : : : ; eαn are algebraically independent over Q. Like the previous formalisation in Coq by Bernard [2], I proceeded by formalising Baker’s alternative formulation of the theorem [1] and then deriving the original one from that. Baker’s version states that for any algebraic numbers β1; : : : ; βn 2 C and distinct algebraic numbers αi; : : : ; αn 2 C, we have: α1 αn β1e + ::: + βne = 0 iff 8i: βi = 0 This has a number of immediate corollaries, e.g.: • e and π are transcendental • ez, sin z, tan z, etc. are transcendental for algebraic z 2 C n f0g • ln z is transcendental for algebraic z 2 C n f0; 1g 1 Contents 1 Divisibility of algebraic integers 3 2 Auxiliary facts about univariate polynomials 6 3 The minimal polynomial of an algebraic number 10 4 The lexicographic ordering on complex numbers 12 5 Additional facts about multivariate polynomials 13 5.1 Miscellaneous ........................... 13 5.2 Converting a univariate polynomial into a multivariate one . 14 6 More facts about algebraic numbers 15 6.1 Miscellaneous ........................... 15 6.2 Turning an algebraic number into an algebraic integer .... 18 6.3 Multiplying an algebraic number with a suitable integer turns it into an algebraic integer. -
Excellence and Uncountable Categoricity of Zilber's Exponential
EXCELLENCE AND UNCOUNTABLE CATEGORICITY OF ZILBER’S EXPONENTIAL FIELDS MARTIN BAYS AND JONATHAN KIRBY Abstract. We prove that Zilber’s class of exponential fields is quasiminimal excellent and hence uncountably categorical, filling two gaps in Zilber’s original proof. 1. Introduction In [Zil05], Zilber defined his exponential fields to be models in a certain class ∗ ECst,ccp. The purpose of this note is to give a proof of the following categoricity theorem, filling gaps in the proof from that paper. ∗ Theorem 1. For each cardinal λ, there is exactly one model Bλ in ECst,ccp of exponential transcendence degree λ, up to isomorphism. Furthermore, the cardinality ∗ of Bλ is λ + ℵ0, so ECst,ccp is categorical in all uncountable cardinals. In particular there is a unique model, B, of cardinality 2ℵ0 and so it makes sense to ask, as Zilber does, whether the complex exponential field Cexp is isomorphic to B. In another paper [BHH+12] we prove a result about quasiminimal excellent classes which gives a way to avoid one of the holes in Zilber’s proof: instead of proving the excellence axiom for this class we show it is redundant by proving it in general. However, we believe that the direct proof given here is of independent interest. In section 2 of this paper we outline the definition of Zilber’s exponential fields, and the concepts of strong extensions and partial exponential subfields. We then give the first-order language in which we work. Section 3 introduces quasiminimal ∗ excellent classes and, largely by reference to Zilber’s work, shows that ECst,ccp sat- isfies all of the axioms except the excellence axiom. -
23. Dimension Dimension Is Intuitively Obvious but Surprisingly Hard to Define Rigorously and to Work With
58 RICHARD BORCHERDS 23. Dimension Dimension is intuitively obvious but surprisingly hard to define rigorously and to work with. There are several different concepts of dimension • It was at first assumed that the dimension was the number or parameters something depended on. This fell apart when Cantor showed that there is a bijective map from R ! R2. The Peano curve is a continuous surjective map from R ! R2. • The Lebesgue covering dimension: a space has Lebesgue covering dimension at most n if every open cover has a refinement such that each point is in at most n + 1 sets. This does not work well for the spectrums of rings. Example: dimension 2 (DIAGRAM) no point in more than 3 sets. Not trivial to prove that n-dim space has dimension n. No good for commutative algebra as A1 has infinite Lebesgue covering dimension, as any finite number of non-empty open sets intersect. • The "classical" definition. Definition 23.1. (Brouwer, Menger, Urysohn) A topological space has dimension ≤ n (n ≥ −1) if all points have arbitrarily small neighborhoods with boundary of dimension < n. The empty set is the only space of dimension −1. This definition is mostly used for separable metric spaces. Rather amazingly it also works for the spectra of Noetherian rings, which are about as far as one can get from separable metric spaces. • Definition 23.2. The Krull dimension of a topological space is the supre- mum of the numbers n for which there is a chain Z0 ⊂ Z1 ⊂ ::: ⊂ Zn of n + 1 irreducible subsets. DIAGRAM pt ⊂ curve ⊂ A2 For Noetherian topological spaces the Krull dimension is the same as the Menger definition, but for non-Noetherian spaces it behaves badly. -
A Non-Slick Proof of the Jordan Hölder Theorem E.L. Lady This Proof Is An
A Non-slick Proof of the Jordan H¨older Theorem E.L. Lady This proof is an attempt to approximate the actual thinking process that one goes through in finding a proof before one realizes how simple the theorem really is. To start with, though, we motivate the Jordan-H¨older Theorem by starting with the idea of dimension for vector spaces. The concept of dimension for vector spaces has the following properties: (1) If V = {0} then dim V =0. (2) If W is a proper subspace of V ,thendimW<dim V . (3) If V =6 {0}, then there exists a one-dimensional subspace of V . (4) dim(S U ⊕ W )=dimU+dimW. W chain (5) If SI i is a of subspaces of a vector space, then dim Wi =sup{dim Wi}. Now we want to use properties (1) through (4) as a model for defining an analogue of dimension, which we will call length,forcertain modules over a ring. These modules will be the analogue of finite-dimensional vector spaces, and will have very similar properties. The axioms for length will be as follows. Axioms for Length. Let R beafixedringandletM and N denote R-modules. Whenever length M is defined, it is a cardinal number. (1) If M = {0},thenlengthM is defined and length M =0. (2) If length M is defined and N is a proper submodule of M ,thenlengthN is defined. Furthermore, if length M is finite then length N<length M . (3) For M =0,length6 M=1ifandonlyifM has no proper non-trivial submodules. -
UC Berkeley UC Berkeley Previously Published Works
UC Berkeley UC Berkeley Previously Published Works Title Operator bases, S-matrices, and their partition functions Permalink https://escholarship.org/uc/item/31n0p4j4 Journal Journal of High Energy Physics, 2017(10) ISSN 1126-6708 Authors Henning, B Lu, X Melia, T et al. Publication Date 2017-10-01 DOI 10.1007/JHEP10(2017)199 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Published for SISSA by Springer Received: July 7, 2017 Accepted: October 6, 2017 Published: October 27, 2017 Operator bases, S-matrices, and their partition functions JHEP10(2017)199 Brian Henning,a Xiaochuan Lu,b Tom Meliac;d;e and Hitoshi Murayamac;d;e aDepartment of Physics, Yale University, New Haven, Connecticut 06511, U.S.A. bDepartment of Physics, University of California, Davis, California 95616, U.S.A. cDepartment of Physics, University of California, Berkeley, California 94720, U.S.A. dTheoretical Physics Group, Lawrence Berkeley National Laboratory, Berkeley, California 94720, U.S.A. eKavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, University of Tokyo, Kashiwa 277-8583, Japan E-mail: [email protected], [email protected], [email protected], [email protected] Abstract: Relativistic quantum systems that admit scattering experiments are quan- titatively described by effective field theories, where S-matrix kinematics and symmetry considerations are encoded in the operator spectrum of the EFT. In this paper we use the S-matrix to derive the structure of the EFT operator basis, providing complementary de- scriptions in (i) position space utilizing the conformal algebra and cohomology and (ii) mo- mentum space via an algebraic formulation in terms of a ring of momenta with kinematics implemented as an ideal. -
Structures Associated with Real Closed Fields and the Axiom Of
Structures Associated with Real Closed Fields and the Axiom of Choice Merlin Carl Abstract An integer part I of a real closed field K is a discretely ordered subring of K with minimal positive element 1 such that, for every x ∈ K, there is i ∈ I with i ≤ x < i + 1. Mourgues and Ressayre showed in [MR] that every real closed field has an integer part. Their construction implicitly uses the axiom of choice. We show that AC is actually necessary to obtain the result by constructing a transitive model of ZF which contains a real closed field without an integer part. Then we analyze some cases where the axiom of choice is not neces- sary for obtaining an integer part. On the way, we demonstrate that a class of questions containing the question whether the axiom of choice is necessary for the proof of a certain ZFC-theorem is algorithmically undecidable. We further apply the methods to show that it is indepen- dent of ZF whether every real closed field has a value group section and a residue field section. This also sheds some light on the possibility to effectivize constructions of integer parts and value group sections which was considered e.g. in [DKKL] and [KL]. 1 Introduction A real closed field (RCF ) K is a field in which −1 is not a sum of squares arXiv:1402.6130v2 [math.LO] 13 Jan 2016 and every polynomial of odd degree has a root. Equivalently, it is elementary equivalent to the field of real numbers in the language of rings. -
Elements of Minimal Prime Ideals in General Rings
Elements of minimal prime ideals in general rings W.D. Burgess, A. Lashgari and A. Mojiri Dedicated to S.K. Jain on his seventieth birthday Abstract. Let R be any ring; a 2 R is called a weak zero-divisor if there are r; s 2 R with ras = 0 and rs 6= 0. It is shown that, in any ring R, the elements of a minimal prime ideal are weak zero-divisors. Examples show that a minimal prime ideal may have elements which are neither left nor right zero-divisors. However, every R has a minimal prime ideal consisting of left zero-divisors and one of right zero-divisors. The union of the minimal prime ideals is studied in 2-primal rings and the union of the minimal strongly prime ideals (in the sense of Rowen) in NI-rings. Mathematics Subject Classification (2000). Primary: 16D25; Secondary: 16N40, 16U99. Keywords. minimal prime ideal, zero-divisors, 2-primal ring, NI-ring. Introduction. E. Armendariz asked, during a conference lecture, if, in any ring, the elements of a minimal prime ideal were zero-divisors of some sort. In what follows this question will be answered in the positive with an appropriate interpretation of \zero-divisor". Two very basic statements about minimal prime ideals hold in a commutative ring R: (I) If P is a minimal prime ideal then the elements of P are zero-divisors, and (II) the union of the minimal prime ideals is M = fa 2 R j 9 r 2 R with ar 2 N∗(R) but r2 = N∗(R)g, where N∗(R) is the prime radical. -
Commutative Algebra
Commutative Algebra Andrew Kobin Spring 2016 / 2019 Contents Contents Contents 1 Preliminaries 1 1.1 Radicals . .1 1.2 Nakayama's Lemma and Consequences . .4 1.3 Localization . .5 1.4 Transcendence Degree . 10 2 Integral Dependence 14 2.1 Integral Extensions of Rings . 14 2.2 Integrality and Field Extensions . 18 2.3 Integrality, Ideals and Localization . 21 2.4 Normalization . 28 2.5 Valuation Rings . 32 2.6 Dimension and Transcendence Degree . 33 3 Noetherian and Artinian Rings 37 3.1 Ascending and Descending Chains . 37 3.2 Composition Series . 40 3.3 Noetherian Rings . 42 3.4 Primary Decomposition . 46 3.5 Artinian Rings . 53 3.6 Associated Primes . 56 4 Discrete Valuations and Dedekind Domains 60 4.1 Discrete Valuation Rings . 60 4.2 Dedekind Domains . 64 4.3 Fractional and Invertible Ideals . 65 4.4 The Class Group . 70 4.5 Dedekind Domains in Extensions . 72 5 Completion and Filtration 76 5.1 Topological Abelian Groups and Completion . 76 5.2 Inverse Limits . 78 5.3 Topological Rings and Module Filtrations . 82 5.4 Graded Rings and Modules . 84 6 Dimension Theory 89 6.1 Hilbert Functions . 89 6.2 Local Noetherian Rings . 94 6.3 Complete Local Rings . 98 7 Singularities 106 7.1 Derived Functors . 106 7.2 Regular Sequences and the Koszul Complex . 109 7.3 Projective Dimension . 114 i Contents Contents 7.4 Depth and Cohen-Macauley Rings . 118 7.5 Gorenstein Rings . 127 8 Algebraic Geometry 133 8.1 Affine Algebraic Varieties . 133 8.2 Morphisms of Affine Varieties . 142 8.3 Sheaves of Functions . -
Arxiv:1012.0864V3 [Math.AG] 14 Oct 2013 Nbt Emtyadpr Ler.Ltu Mhsz H Olwn Th Following the Emphasize Us H Let Results Cit.: His Algebra
ORLOV SPECTRA: BOUNDS AND GAPS MATTHEW BALLARD, DAVID FAVERO, AND LUDMIL KATZARKOV Abstract. The Orlov spectrum is a new invariant of a triangulated category. It was intro- duced by D. Orlov building on work of A. Bondal-M. van den Bergh and R. Rouquier. The supremum of the Orlov spectrum of a triangulated category is called the ultimate dimension. In this work, we study Orlov spectra of triangulated categories arising in mirror symmetry. We introduce the notion of gaps and outline their geometric significance. We provide the first large class of examples where the ultimate dimension is finite: categories of singular- ities associated to isolated hypersurface singularities. Similarly, given any nonzero object in the bounded derived category of coherent sheaves on a smooth Calabi-Yau hypersurface, we produce a new generator by closing the object under a certain monodromy action and uniformly bound this new generator’s generation time. In addition, we provide new upper bounds on the generation times of exceptional collections and connect generation time to braid group actions to provide a lower bound on the ultimate dimension of the derived Fukaya category of a symplectic surface of genus greater than one. 1. Introduction The spectrum of a triangulated category was introduced by D. Orlov in [39], building on work of A. Bondal, R. Rouquier, and M. van den Bergh, [44] [11]. This categorical invariant, which we shall call the Orlov spectrum, is simply a list of non-negative numbers. Each number is the generation time of an object in the triangulated category. Roughly, the generation time of an object is the necessary number of exact triangles it takes to build the category using this object.