DOCSLIB.ORG

Introduction to Commutative Algebra and Algebraic Geometry

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Introduction to Commutative Algebra and Algebraic Geometry INTRODUCTION TO COMMUTATIVE ALGEBRA AND ALGEBRAIC GEOMETRY. The purpose of these notes is to give a quick and relatively painless introduc- tion to the language of modern commutative algebra and algebraic geometry. The point of view which we will emphasize is that commutative algebra and algebraic geometry (at least the local theory) are two different languages for talking about the same thing. The algebraic and the geometric aspects of every phenomenon will be introduced and discussed concurrently. The first part of the course will consist of standard material; towards the end we will treat some topics of current inter- est such as valuation theory and singularities. Due to spacetime limitations, we will omit some important topics, notably cohomology, traditionally present in an introductory course. Unless otherwise stated, all rings in these notes will be commutative with 1. N will denote the set of natural numbers, N0 the set of non-negative integers. 1. Varieties and ideals. § Let k be a field and x1,...,xn independent variables. The following are some basic examples of rings appearing in algebraic, analytic and formal geometry. The reader should keep them in mind in order to test and illustrate the general theory. (1) Polynomial rings k[x1,...,xn] and D[x1,...,xn], where D = Z or, more generally, D is the ring of integers in some number field, such as Z[√2] or Z[√5i]. (2) Formal power series rings k[[x ,...,x ]] := c xα1 xα2 ...xαn α =(α ,...,α ) and c k 1 n α 1 2 n 1 n α ∈ α∈Nn X0 and Zp[[x1,...,x n]], where p is a prime number and Zp is the ring of p-adic integers. (3) Convergent power series rings C x1,...,xn and Zp x1,...,xn . { } { } The beauty and power of commutative algebra lie in the fact that, it provides a universal language and methods for studying number theory, local algebraic geom- etry and local questions in complex analysis, as illustrated by the above examples. Given rings R and S, a homomorphism from R to S is a map R S which preserves the ring operations + and . → · Typeset by AMS-TEX 1 2 INTRODUCTION TO COMMUTATIVE ALGEBRA AND ALGEBRAIC GEOMETRY. Definition 1.1. Let R be a ring and I a non-empty subset of R. I is an ideal of R if I is closed under addition and for any a R, x I, we have ax I. ∈ ∈ ∈ For example, 0 is an ideal (usually denoted by (0)); the entire ring R is also an ideal, sometimes{ } called the unit ideal and denoted by (1). Let B = eλ λ∈Λ be a subset of R. Let BR denote the set of all linear combina- tions of the{ form} n BR = eλi bλi bλi R, eλi B, n N . | ∈ ∈ ∈ (i=1 ) X Exercise 1. If I = BR, prove that I is the smallest ideal of R containing B. If I = BR, we say that I is the ideal generated by B, or that B is a set of generators or a base of I. Of course, a given ideal I may have many different sets of generators. An ideal I is said to be finitely generated if it has a finite set of generators. Definition 1.2. A ring R is Noetherian if every ascending chain I I I ... 1 ⊂ 2 ⊂ 3 ⊂ of ideals of R stabilizes, that is, there exists n0 N such that In = In for all n>n0. ∈ 0 Exercise 2. Prove that a ring R is Noetherian if and only if every ideal of R is finitely generated. Commutative algebra grew out of number theory and geometric invariant theory at the turn of the century. One of the starting points was Hilbert’s basis theorem: Theorem 1.3. Let R be a Noetherian ring and x1,...,xn independent variables. Then R[x1,...,xn] is also Noetherian for any n. Proof. It is sufficient to consider the case n = 1. We want to establish that R[x] is Noetherian, provided R is Noetherian. Let I be an ideal of R[x]. Let J denote the ideal of R, consisting of all the leading coefficients of elements of I (the reader should check that J is, indeed, an ideal). Since R is Noetherian, J is finitely generated. Hence there exists a finite collection of polynomials f ,...,f R[x], whose leading 1 m ∈ coefficients generate J. Let d = max deg fi. Then for every f I such that 1≤i≤m ∈ m deg f d, there exist h1,...,hm R[x] such that i=1 hifi has the same degree and leading≥ coefficient as f, in other∈ words, P m (1.1) deg f h f < deg f. − i i i=1 ! X Applying (1.1) repeatedly and using induction on deg f, we can find g1,...,gs R[x] such that ∈ m (1.2) deg f g f < d. − i i i=1 ! X INTRODUCTION TO COMMUTATIVE ALGEBRA AND ALGEBRAIC GEOMETRY. 3 By (1.2), there exists the smallest l N0 having the following property. There exist ∈ r N, f1,...,fr I such that for any f I there are g1,...,gr R[x] satisfying ∈ ∈ ∈ ∈ r (1.3) deg f g f <l − i i i=1 ! X (where, by convention, we take deg 0 to be 1). − Now, suppose I is not finitely generated. Then l > 0. Let Il denote the set of those elements of I which have degree exactly l 1. Let J denote the ideal − l of R consisting of 0 and all the leading coefficients of elements of Il. Since R is Noetherian, Jl is finitely generated. Hence there exist finitely many elements fr+1,...,fs of Il, such that for every f Il there exist gr+1,...,gs R satisfying s ∈ ∈ deg f g f < l 1. In view of (1.3), this contradicts the minimality of − i i − i=r+1 l. P Corollary 1.4. Let k be a field and x1,...,xn independent variables. Then the polynomial ring k[x1,...,xn] is Noetherian. Similarly for Z[x1,...,xn]. Let R be a ring and I an ideal of R. The quotient of R by I is the set of R cosets I (viewed as abelian groups with respect to +), endowed with the obvious R ring operations. We have the natural surjective homomorphism R I , whose R → kernel is I. We also say that I is a homomorphic image of R. Note also that every surjective ring homomorphism π : R S is the quotient of R by some ideal (namely, by Ker π). → We are now ready to introduce our basic dictionary between algebra and geome- try, at first in the classical setting with algebraic varieties on the geometric side and finitely generated algebras over a field on the algebraic side. Soon we will switch to the more general modern setting with arbitrary schemes on the geometric side and arbitrary rings on the algebraic side. Classically, algebraic geometry studied algebraic subvarieties of kn (i.e. subsets of kn defined by finitely many polynomial equations), where k is a field and n N. ∈ In fact, k was usually taken to be C. Definition 1.5. Let k be a field and let I be an ideal of k[x1,...,xn]. The alge- braic variety defined by I in kn is V (I) = a kn f(a)=0 for all f I . { ∈ | ∈ } Since k[x1,...,xn] is Noetherian, we can choose a finite base (f1,...,fm) for I, so that V (I) = a kn f (a) = = f (a)=0 . { ∈ | 1 ··· m } Associated to every ideal I of k[x1,...,xn] we have the algebraic variety V (I). Conversely, given any set V kn, we may consider the ideal I(V ) defined by I(V ) = f k[x ,...,x ] f⊂(a) = 0 for all a V . A natural quesiton arises: { ∈ 1 n | ∈ } 4 INTRODUCTION TO COMMUTATIVE ALGEBRA AND ALGEBRAIC GEOMETRY. what is the relation between I and I(V (I))? To answer this question, we need another definition. Definition 1.6. Let R be a ring and I an ideal of R. The radical of I , denoted by √I, is defined to be n √I = x R there exists n N0 such that x I . { ∈ | ∈ ∈ } We say that I is radical if I = √I. Exercise 3. Prove that √I is an ideal and that I √I. ⊂ Let k be a field and I an ideal of k[x1,...,xn]. Clearly, V (I) = V (√I). It is also clear that I I(V (I)) for any ideal I k[x ,...,x ]. Hence for any ideal I, ⊂ ⊂ 1 n √I I(V (√I)) = I(V (I)). It turns out that if k is an algebraically closed field (this means⊂ that every non-constant polynomial in k[x] has a root in k), we always have √I = I(V (I)). This is a non-trivial theorem, called Hilbert’s Nullstellensatz. We will state and prove several versions of the Nullstellensatz, all of which are sometimes referred to by this name. Theorem 1.7 (The strong form of Hilbert’s Nullstellensatz). Let k be an algebraically closed field and I an ideal of R = k[x1,...,xn]. Then I(V (I)) = √I. In other words, √I = f R f(a)=0 a V (I) . { ∈ | ∀ ∈ } In other words, there is a one-to-one correspondence between algebraic subvari- n eties of k and radical ideals of k[x1,...,xn]. A proof of Hilbert’s Nullstellensatz will be given shortly. First, we would like to advance a little more in our task of constructing a dictionary between algebra and geometry.
Load more

Recommended publications
  • Ring (Mathematics) 1 Ring (Mathematics)
    Ring (mathematics) 1 Ring (mathematics) In mathematics, a ring is an algebraic structure consisting of a set together with two binary operations usually called addition and multiplication, where the set is an abelian group under addition (called the additive group of the ring) and a monoid under multiplication such that multiplication distributes over addition.a[›] In other words the ring axioms require that addition is commutative, addition and multiplication are associative, multiplication distributes over addition, each element in the set has an additive inverse, and there exists an additive identity. One of the most common examples of a ring is the set of integers endowed with its natural operations of addition and multiplication. Certain variations of the definition of a ring are sometimes employed, and these are outlined later in the article. Polynomials, represented here by curves, form a ring under addition The branch of mathematics that studies rings is known and multiplication. as ring theory. Ring theorists study properties common to both familiar mathematical structures such as integers and polynomials, and to the many less well-known mathematical structures that also satisfy the axioms of ring theory. The ubiquity of rings makes them a central organizing principle of contemporary mathematics.[1] Ring theory may be used to understand fundamental physical laws, such as those underlying special relativity and symmetry phenomena in molecular chemistry. The concept of a ring first arose from attempts to prove Fermat's last theorem, starting with Richard Dedekind in the 1880s. After contributions from other fields, mainly number theory, the ring notion was generalized and firmly established during the 1920s by Emmy Noether and Wolfgang Krull.[2] Modern ring theory—a very active mathematical discipline—studies rings in their own right.
    [Show full text]
  • A Brief History of Ring Theory
    A Brief History of Ring Theory by Kristen Pollock Abstract Algebra II, Math 442 Loyola College, Spring 2005 A Brief History of Ring Theory Kristen Pollock 2 1. Introduction In order to fully define and examine an abstract ring, this essay will follow a procedure that is unlike a typical algebra textbook. That is, rather than initially offering just definitions, relevant examples will first be supplied so that the origins of a ring and its components can be better understood. Of course, this is the path that history has taken so what better way to proceed? First, it is important to understand that the abstract ring concept emerged from not one, but two theories: commutative ring theory and noncommutative ring the- ory. These two theories originated in different problems, were developed by different people and flourished in different directions. Still, these theories have much in com- mon and together form the foundation of today's ring theory. Specifically, modern commutative ring theory has its roots in problems of algebraic number theory and algebraic geometry. On the other hand, noncommutative ring theory originated from an attempt to expand the complex numbers to a variety of hypercomplex number systems. 2. Noncommutative Rings We will begin with noncommutative ring theory and its main originating ex- ample: the quaternions. According to Israel Kleiner's article \The Genesis of the Abstract Ring Concept," [2]. these numbers, created by Hamilton in 1843, are of the form a + bi + cj + dk (a; b; c; d 2 R) where addition is through its components 2 2 2 and multiplication is subject to the relations i =pj = k = ijk = −1.
    [Show full text]
  • 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 .
    [Show full text]
  • RING THEORY 1. Ring Theory a Ring Is a Set a with Two Binary Operations
    CHAPTER IV RING THEORY 1. Ring Theory A ring is a set A with two binary operations satisfying the rules given below. Usually one binary operation is denoted `+' and called \addition," and the other is denoted by juxtaposition and is called \multiplication." The rules required of these operations are: 1) A is an abelian group under the operation + (identity denoted 0 and inverse of x denoted x); 2) A is a monoid under the operation of multiplication (i.e., multiplication is associative and there− is a two-sided identity usually denoted 1); 3) the distributive laws (x + y)z = xy + xz x(y + z)=xy + xz hold for all x, y,andz A. Sometimes one does∈ not require that a ring have a multiplicative identity. The word ring may also be used for a system satisfying just conditions (1) and (3) (i.e., where the associative law for multiplication may fail and for which there is no multiplicative identity.) Lie rings are examples of non-associative rings without identities. Almost all interesting associative rings do have identities. If 1 = 0, then the ring consists of one element 0; otherwise 1 = 0. In many theorems, it is necessary to specify that rings under consideration are not trivial, i.e. that 1 6= 0, but often that hypothesis will not be stated explicitly. 6 If the multiplicative operation is commutative, we call the ring commutative. Commutative Algebra is the study of commutative rings and related structures. It is closely related to algebraic number theory and algebraic geometry. If A is a ring, an element x A is called a unit if it has a two-sided inverse y, i.e.
    [Show full text]
  • NOTES in COMMUTATIVE ALGEBRA: PART 1 1. Results/Definitions Of
    NOTES IN COMMUTATIVE ALGEBRA: PART 1 KELLER VANDEBOGERT 1. Results/Definitions of Ring Theory It is in this section that a collection of standard results and definitions in commutative ring theory will be presented. For the rest of this paper, any ring R will be assumed commutative with identity. We shall also use "=" and "∼=" (isomorphism) interchangeably, where the context should make the meaning clear. 1.1. The Basics. Definition 1.1. A maximal ideal is any proper ideal that is not con- tained in any strictly larger proper ideal. The set of maximal ideals of a ring R is denoted m-Spec(R). Definition 1.2. A prime ideal p is such that for any a, b 2 R, ab 2 p implies that a or b 2 p. The set of prime ideals of R is denoted Spec(R). p Definition 1.3. The radical of an ideal I, denoted I, is the set of a 2 R such that an 2 I for some positive integer n. Definition 1.4. A primary ideal p is an ideal such that if ab 2 p and a2 = p, then bn 2 p for some positive integer n. In particular, any maximal ideal is prime, and the radical of a pri- mary ideal is prime. Date: September 3, 2017. 1 2 KELLER VANDEBOGERT Definition 1.5. The notation (R; m; k) shall denote the local ring R which has unique maximal ideal m and residue field k := R=m. Example 1.6. Consider the set of smooth functions on a manifold M.
    [Show full text]
  • Commutative Algebra with a View Toward Algebraic Geometry, by David Eisenbud, Graduate Texts in Math., Vol
    BULLETIN (New Series) OF THE AMERICAN MATHEMATICAL SOCIETY Volume 33, Number 3, July 1996 Commutative algebra with a view toward algebraic geometry, by David Eisenbud, Graduate Texts in Math., vol. 150, Springer-Verlag, Berlin and New York, 1995, xvi+785 pp., $69.50, ISBN 0-387-94268-8 In the title of a story [To] written in 1886, Tolstoy asks, “How Much Land Does a Man Need?” and answers the question: just enough to be buried in. One may ask equally well, “How much algebra does an algebraic geometer—man or woman—need?” and prospective algebraic geometers have been known to worry that Tolstoy’s answer remains accurate. Authors of textbooks have at times given vastly different answers, albeit with a general tendency over time to be monotonely increasing in what they expect will be useful. In crudely quantitative terms, one has at one extreme the elegant minimalist introduction of Atiyah and Macdonald [AM] at 128 pages, then Nagata [Na] at 234 pages, Matsumura [Ma] at 316 pages, Zariski and Samuel [ZS] at 743 pages, and the present work at 785 pages. I suspect that most of my fellow algebraic geometers, as a practical matter, would answer my question by saying, “Enough to read Hartshorne.” Hartshorne’s Algebraic geometry [Ha], appearing in 1977, rapidly became the central text from which recent generations of algebraic geometers have learned the essential tools of their subject in the aftermath of the “French revolution” inspired by the work of Grothendieck and Serre (Principles of algebraic geometry by Griffiths and Har- ris [GH] plays a comparable role on the geometric side for the infusion of com- plex analytic techniques entering algebraic geometry at about the same period).
    [Show full text]
  • Introduction to Commutative Algebra
    MATH 603: INTRODUCTION TO COMMUTATIVE ALGEBRA THOMAS J. HAINES 1. Lecture 1 1.1. What is this course about? The foundations of differential geometry (= study of manifolds) rely on analysis in several variables as \local machinery": many global theorems about manifolds are reduced down to statements about what hap- pens in a local neighborhood, and then anaylsis is brought in to solve the local problem. Analogously, algebraic geometry uses commutative algebraic as its \local ma- chinery". Our goal is to study commutative algebra and some topics in algebraic geometry in a parallel manner. For a (somewhat) complete list of topics we plan to cover, see the course syllabus on the course web-page. 1.2. References. See the course syllabus for a list of books you might want to consult. There is no required text, as these lecture notes should serve as a text. They will be written up \in real time" as the course progresses. Of course, I will be grateful if you point out any typos you find. In addition, each time you are the first person to point out any real mathematical inaccuracy (not a typo), I will pay you 10 dollars!! 1.3. Conventions. Unless otherwise indicated in specific instances, all rings in this course are commutative with identity element, denoted by 1 or sometimes by e. We will assume familiarity with the notions of homomorphism, ideal, kernels, quotients, modules, etc. (at least). We will use Zorn's lemma (which is equivalent to the axiom of choice): Let S; ≤ be any non-empty partially ordered set.
    [Show full text]
  • Math 746 — Commutative Algebra — Spring 2021 Instructor: Alexander Duncan
    Math 746 | Commutative Algebra | Spring 2021 Instructor: Alexander Duncan Commutative algebra is the study of commutative rings, which are ubiquitous in all areas of mathematics. Indeed, it is a formidable challenge to solve problems without using integers or polynomials. This course arms you with the basic concepts and techniques of the subject. This will serve as a foundation for both its applications in other areas of mathematics and for deeper study of the subject itself. The subject's history is intimately involved with number theory | many of the bedrock notions such as ideals, integral extensions, valuations, and completions were first developed to study primes and the integers. The 20th century saw algebraic ge- ometry completely rewritten from the ground up with commutative algebra its lingua franca. The subject revolutionized geometry and topology, which returned the favor with new tools like homology theory. Now, the burgeoning field of algebraic combi- natorics studies the relationship of combinatorial objects like matroids and polytopes with algebraic objects like monomial ideals. @ @ @ @ ···! F4 −! F3 −! F2 −! F1 −! F0 ! 0 The textbook is A Term of Commutative Algebra by A. Altman and S. Kleiman, which is available for free online. This text is a modern take on the venerable classic Atiyah & Macdonald. Despite its name, I do not expect to cover all the material in the text in one semester. However, topics we will see include: • rings and modules • homological algebra • limits • tensor products • localization • integral extensions • primary decomposition • valuation rings The prerequisite for the course is Math 701. You should have at least seen rings, ideals, and modules before, but you are not expected to be fluent (yet).
    [Show full text]
  • Open Problems in Commutative Ring Theory
    Open problems in commutative ring theory Paul-Jean Cahen , Marco Fontana y, Sophie Frisch zand Sarah Glaz x December 23, 2013 Abstract This article consists of a collection of open problems in commuta- tive algebra. The collection covers a wide range of topics from both Noetherian and non-Noetherian ring theory and exhibits a variety of re- search approaches, including the use of homological algebra, ring theoretic methods, and star and semistar operation techniques. The problems were contributed by the authors and editors of this volume, as well as other researchers in the area. Keywords: Prüfer ring, homological dimensions, integral closure, group ring, grade, complete ring, McCoy ring, Straight domain, di- vided domain, integer valued polynomials, factorial, density, matrix ring, overring, absorbing ideal, Kronecker function ring, stable ring, divisorial domain, Mori domain, finite character, PvMD, semistar operation, star operation, Jaffard domain, locally tame domain, fac- torization, spectrum of a ring, integral closure of an ideal, Rees al- gebra, Rees valuation. Mthematics Subject Classification (2010): 13-02; 13A05; 13A15; 13A18; 13B22; 13C15; 13D05; 13D99; 13E05; 13F05; 13F20; 13F30; 13G05 1 Introduction This article consists of a collection of open problems in commutative algebra. The collection covers a wide range of topics from both Noetherian and non- Noetherian ring theory and exhibits a variety of research approaches, including Paul-Jean Cahen (Corresponding author), 12 Traverse du Lavoir de Grand-Mère, 13100 Aix en Provence, France. e-mail: [email protected] yMarco Fontana, Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, Largo San Leonardo Murialdo 1, 00146 Roma, Italy. e-mail: [email protected] zSophie Frisch, Mathematics Department, Graz University of Technology, Steyrergasse 30, 8010 Graz, Austria.
    [Show full text]
  • MATH0021 Commutative Algebra
    MATH0021 Commutative Algebra Year: 2021{2022 Code: MATH0021 Level: 6 (UG) Normal student group(s): UG: Year 3 Mathematics degrees Value: 15 credits (= 7.5 ECTS credits) Term: 2 Assessment: 100% examination Normal Pre-requisites: MATH0053 Lecturer: Prof FEA Johnson Course Description and Objectives Rings are the basic mathematical entities in which we calculate. The most elementary examples are fields and the resulting theory is completely covered in the algebra courses in years 1 and 2. In this course we study linear algebra over more general commutative rings;here the notion of `vector space over a field’ is replaced by that of `module over a ring'. In this wider context many of the familiar aspects of linear algebra require modification. For example the `basis theorem' for vector spaces is replaced by the notion of `free resolution' for more general modules. We will concentrate on a class of `well behaved' rings, the so called Noetherian rings. Examples are the rings F[t1; : : : ; tn], Z[t1; : : : ; tn] of polynomials over a field F and integers Z. As an analogue and modification of the Jordan Normal Form Theorem we shall classify modules over Principal Ideal Domains (PIDs). A special case is the classification theorem for finitely generated abelian groups. We shall introduce the notion of the `dimension of a ring'. This indicates how far from being a field a given ring is. Thus fields have dimension 0, Z has dimension 1, whilst the polynomial ring Z[t1; : : : ; tn] has dimension n + 1. This course will provide a solid foundation of commutative rings and module theory, as well as help developing foundational notions helpful in other areas such as number theory, algebraic geometry, and homological algebra.
    [Show full text]
  • Commutative Algebra
    A course in Commutative Algebra Taught by N. Shepherd-Barron Michaelmas 2012 Last updated: May 31, 2013 1 Disclaimer These are my notes from Nick Shepherd-Barron's Part III course on commutative algebra, given at Cambridge University in Michaelmas term, 2012. I have made them public in the hope that they might be useful to others, but these are not official notes in any way. In particular, mistakes are my fault; if you find any, please report them to: Eva Belmont [email protected] Contents 1 October 55 Noetherian rings, Hilbert's Basis Theorem, Fractions 2 October 86 Localization, Cayley-Hamilton, Nakayama's Lemma, Integral elements 3 October 10 10 Integral extensions in finite separable field extensions, OX is f.g./Z, Going up theorem, Noether normalization, Weak Nullstellensatz 4 October 12 13 Strong Nullstellensatz, more on integrality and field extensions Saturday optional class { October 13 16 5 October 15 16 p T T Primary ideals, I = primary (if Noetherian), I = Pi uniquely, Artinian rings have finitely many primes and all primes are maximal 6 October 17 19 Finite length modules; conditions under which Noetherian () Artinian, etc.; Artinian = L Artinian local 7 October 19 22 Artinian local rings; DVR's and properties; local Noetherian domains of height 1 Saturday optional lecture { October 20 24 8 October 22 26 9 October 24 29 10 October 26 32 Saturday optional lecture { October 27 36 11 October 29 39 12 October 31 41 13 November 2 44 Saturday optional lecture { November 3 48 14 November 5 50 15 November 7 52 16 November 9 55 Saturday optional lecture { November 10 57 17 November 12 60 18 November 14 62 19 November 16 65 20 November 17 67 21 November 19 70 22 November 21 73 23 November 23 75 24 November 24 78 Commutative algebra Lecture 1 Lecture 1: October 5 Chapter 1: Noetherian rings Definition 1.1.
    [Show full text]
  • Limits in Commutative Algebra and Algebraic Geometry
    Commutative Algebra and Noncommutative Algebraic Geometry, I MSRI Publications Volume 67, 2015 Limits in commutative algebra and algebraic geometry STEVEN DALE CUTKOSKY In this survey article we explore various limits and asymptotic properties in commutative algebra and algebraic geometry. We show that several important invariants have good asymptotic behavior. We develop this and give some examples of pathological behavior for topics such as multiplicity of graded families of ideals, volumes of line bundles on schemes and regularity of powers of ideals. 1. Introduction This article is on the general theme of limits arising in commutative algebra and algebraic geometry, in asymptotic multiplicity and rgularity. The four sections of this article are based on the four talks that I gave during the Spring semester of the special year on Commutative Algebra, held at MSRI during the 2012–2013 academic year. The first section is based on an Evans lecture I gave at Berkeley. 2. Asymptotic multiplicities Multiplicity and projection from a point. We begin by discussing a formula involving the multiplicity of a point on a variety, which evolved classically. Proofs of the formula (1) can be found in Theorem 5.11 of[Mumford 1976] (over k D C), in Section 11 of[Abhyankar 1998], Section 12 of[Lipman 1975] and Theorem 12.1[Cutkosky 2009]. N N Suppose that k D k is an algebraically closed field and X ⊂ Pk is a d- dimensional projective variety. The degree of X is defined as #.X \ L N−d / where L N−d is a generic linear subspace of PN of dimension N − d.
    [Show full text]