Questions tagged [regular-rings]

For questions regarding a commutative Noetherian ring whose localization at each prime ideal is a regular local ring.

We say that a commutative Noetherian ring $R$ is regular whenever its localization at every prime ideal $P$ is a regular local ring $(R_P, P R_P, k(P))$ in the sense that the Krull dimension of $R_P$ is equal to the unique number of generators of the maximal ideal $P R_P$ of $R_P,$ i.e., we have that $$\dim R_P = \mu(P R_P) = \dim_{k(P)} \frac{P R_P}{(P R_P)^2},$$ where $\dim R_P$ is Krull dimension, and the second dimension is the $k(P)$-vector space dimension.

Regular rings enjoy a wealth of desirable properties, one of the most fundamental of which is that every localization of a regular ring is a regular local ring. Every field is a regular ring of Krull dimension zero. Further, a polynomial ring $k[x_1, \dots, x_n]$ over a field is a regular ring of Krull dimension $n.$ Dedekind domains are another common example of regular rings.

89 questions
6
votes
0 answers

Regular local ring if every maximal Cohen-Macaulay module is free

I have a problem like this "Let $R$ be a Cohen-Macaulay local ring, $\dim R=d$. Given that every maximal Cohen-Macaulay $R$-module is free, prove that $R$ is a regular local ring." My lecturer gave me a hint to use the Auslander-Buchsbaum theorem:…
5
votes
1 answer

A sandwich theorem for local rings

The following question seems natural to ask in view of this question and its comments/answers: Let $R \subseteq S$ be commutative Noetherian rings, let $q$ be a maximal ideal of $S$, $p$ a maximal of $R$ and $p=R \cap q$. The localization of $R$ at…
5
votes
0 answers

On a special kind of local Gorenstein ring of dimension $2$

Let $(R, \mathfrak m,k)$ be a local Gorenstein ring of dimension $2$ such that $\mu (\mathfrak m^2)(=\dim_k \mathfrak m^2/\mathfrak m^3) =3$ . Then is it true that $R$ is regular ? Or at least is it true that $R$ has minimal multiplicity i.e.…
4
votes
1 answer

Cohen-Macaulayness and regularity of $A/p$

This question claimed (and proved) that if $p$ is a prime ideal of $A=k[x_1,\ldots,x_n]$ with $\operatorname{ht}(p) \in \{0,1,n-1,n\}$, then $A/p$ is Cohen-Macaulay. Now, let $A$ be a (Noetherian) UFD of Krull dimension $n$ which is…
4
votes
1 answer

A local Cohen-Macaulay ring whose dimension is one less than the minimal no. of generators of its maximal ideal

Let $(R, \mathfrak m)$ be a local Cohen-Macaulay ring. If $\dim R=\mu (\mathfrak m)-1$ , then is it true that $R \cong S/(f)$ for some regular local ring $S$ and some (non-invertible) regular element $f \in S$ (note that since $S$ is a domain, any…
4
votes
1 answer

Polynomial rings are regular

I want to use the result that the polynomial ring $R:=k[x_1,\cdots,x_n]$ is a regular ring. I can prove that every maximal ideal $\mathfrak m$ in $R$ can be generated by $n$ number of elements so that $R_{\mathfrak m}$ is a regular local ring. Now…
user436053
4
votes
1 answer

When does an integral group ring have finite global dimension?

Let $G$ be a finite group and $R=\mathbb{Z}[G]$ the integral group ring. If $G$ is such that $R$ is Noetherian (so $G$ polycyclic-by-finite) when does $R$ have finite global dimension? Another way of asking the question is, when is $R$ regular?
4
votes
1 answer

Normality of localizations in polynomial rings?

Normality of a ring here refers to being equal to it's integral closure in it's field of fractions. The problem is: Let $A=\mathbb{C}[x,y]/(y^2-x^3-x^2)$. Show that $A_m$ is normal for every maximal ideal $m\subset A$, except for $m=(x,y)$ in $A$.…
3
votes
0 answers

motivation for regular schemes

Clearly regular schemes are like smooth varieties (in the sense of dimension of tangent spaces) and should be very important in algebraic geometry. Is there any big theorem focusing on regular schemes? Is there any property of regular scheme that…
Z Wu
  • 2,099
3
votes
1 answer

$\operatorname {Ext}$ vanishing and finitely generated reflexive modules over regular local rings

Let $M$ be a finitely generated reflexive module over a regular local ring $(R,\mathfrak m,k)$ such that $\operatorname {Ext}^1_R( \operatorname {Hom}_R(M,M),R)=0$. Then how to show that $M$ is a free $R$-module ? Here reflexive means…
3
votes
0 answers

Prove polynomial ring over a discrete valuation ring quotient by powers of maximal ideal is regular?

Let $(R,\mathfrak{m},k)$ be a discrete valuation ring, (of characteristic $p$ if you need). Let $n\geq 1$ be an integer. Is the ring $\frac{R}{\mathfrak{m}^n}[x]$ regular? Note that: Regularity can be checked at localisation of maximal ideals.
3
votes
2 answers

Regular ring not UFD

I have to prove that the ring $R=K[x,y]/(x^2-y^3+y)$ is not a UFD showing that the prime ideal $(x,y)R$ has height 1, but it's not principal. Do someone know a simple way to prove it? I know there are others way to solve the problem, for example…
3
votes
1 answer

Regular local rings are UFD

For 1-dimensional case, regular local implies PID and hence UFD. That is clear and geometry wise it is basically looking at the germs of smooth functions at a point. For higher dimensional case, what is the geometrical reason that causes regular…
3
votes
1 answer

Why does Hartshorne have hypothesis $(*)$ in II.6?

In Hartshorne's chapter on Weil divisors he fixes the following hypothesis: $(*)$ Every scheme is Noetherian , integral, separated, and regular in codimension 1 I can understand why you would want the first three hypotheses, but the regularity in…
54321user
  • 3,383
3
votes
0 answers

Do flat morphism of schemes induce injection on cotangents?

In the proof that an étale morphism induces an isomorphism on tangents, we use the fact that, if the morphism is unramified, then the induced map on cotangents is surjective. Then we conclude using flatness. Something I can't get from the proof is…
W.Rether
  • 3,180
1
2 3 4 5 6