Math 2.0

Commutative algebra Definition

Regular local ring

Builds on Local ringNoetherian ringKrull dimensionEmbedding dimension

Definition

Let (R,𝔪)(R, \mathfrak m) be a Noetherian local ring with residue field k=R/𝔪k = R/\mathfrak m, and let d=dim⁡Rd = \dim R be its Krull dimension. The ring RR is regular if 𝔪\mathfrak m can be generated by dd elements. Equivalently, RR is regular if its embedding dimension dim⁡k𝔪/𝔪2\dim_k \mathfrak m / \mathfrak m^2 equals dd.

Remarks

A set of dd generators of 𝔪\mathfrak m in a regular local ring is called a regular system of parameters.

Example: a field is regular, with d=0d = 0 and 𝔪=0\mathfrak m = 0. A Noetherian local domain of dimension 11 is regular exactly when 𝔪\mathfrak m is principal, that is, when it is a discrete valuation ring, such as ℤ(p)\Z_{(p)}. For a field kk, the rings k[x1,…,xn](x1,…,xn)k[x_1, \ldots, x_n]_{(x_1, \ldots, x_n)} and k[ ⁣[x1,…,xn] ⁣]k[\![x_1, \ldots, x_n]\!] have dimension nn and maximal ideal generated by the nn elements x1,…,xnx_1, \ldots, x_n, so they are regular.

Non-example: R=k[x]/(x2)R = k[x]/(x^2) has dimension 00, but its maximal ideal (x)≠0(x) \ne 0 needs one generator, so it is not regular. The cusp k[x,y](x,y)/(y2−x3)k[x, y]_{(x, y)}/(y^2 - x^3) has dimension 11 and embedding dimension 22, so it is not regular.

Reading path

To understand this page from the ground up, read these 5 pages in order. The foundations come first.

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Each page uses the pages above it. The colour of the bar on a box shows how strong the evidence is, and the box also gives it as text. The list has the same pages.
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  1. Embedding dimension concept
  2. Krull dimension concept
  3. Local ring concept
  4. Noetherian ring concept
  5. Regular local ring definition

Further reading

  1. Web https://en.wikipedia.org/wiki/Regular_local_ring
About this page
TagKTQC33ZJTN
URIm2://KTQC33ZJTN
Kinddefinition
WritingW0 stub
MSC13H05
DefinesRegular local ring
UsesLocal ring, Noetherian ring, Krull dimension, Embedding dimension
Changed2 November 2026

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