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Commutative rings, modules, ideals, homological algebra, computational aspects, invariant theory, connections to algebraic geometry and combinatorics.

2 votes

Grade is not equal to injective dimension

https://math.stackexchange.com/questions/3459133/quotient-of-a-local-cohen-macaulay-ring-by-a-minimal-prime gives example of a local Gorenstein ring $R$ with a minimal prime ideal $P$ such that $R/P$ …
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6 votes
1 answer
322 views

When can we choose non-zero-divisor $x\in \mathfrak m$ in a reduced local ring $(R,\mathfrak...

Let $(R,\mathfrak m)$ be a local Cohen-Macaulay reduced ring of dimension at least $2$. Then, can we find a non-zero-divisor $x\in \mathfrak m$ such that $R/xR$ is again a reduced ring? If needed, I a …
Alex's user avatar
  • 480
2 votes
1 answer
196 views

Localization of quasi-excellent rings are quasi-excellent?

If $R$ is a quasi-excellent ring, then is $R_{\mathfrak p}$ also quasi-excellent for every prime ideal $\mathfrak p$ of $R$ ? I think Matsumura's commutative ring theory book says that localization of …
Alex's user avatar
  • 480
2 votes
0 answers
73 views

From exact triangles in the stable category of maximal Cohen--Macaulay modules to short exac...

Let $R$ be a local Gorenstein ring. Let $\underline{\text{CM}}(R)$ be the stable category of maximal Cohen--Macaulay modules, it is known to carry a triangulated structure. My question is: If $M\to N\ …
Alex's user avatar
  • 480
1 vote
0 answers
84 views

Is $(I(R:_{Q(R)} I))^n$ generated by $(fI)^n$ as $f$ varies over $(R:_{Q(R)} I)$?

Let $(R, \mathfrak m)$ be a Noetherian local domain of dimension $1$ which is not a UFD. Let $Q(R)$ be the fraction field of $R$. If $I\subsetneq \mathfrak m$ is a non-zero, non-principal ideal of $R$ …
Alex's user avatar
  • 480
2 votes
0 answers
72 views

Sum of Betti numbers and certain short exact sequence of modules of finite length over regul...

Let $N$ be a module of finite length over a regular local ring $R$ of characteristic $0$. Let $M$ be an $R$-module which fits into a short exact sequence $0\to N^{\oplus a}\to M \to N^{\oplus b}\to 0$ …
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  • 480
1 vote
0 answers
78 views

Localization of totally acyclic complex or projective modules remain totally acyclic?

Let $R$ be a commutative Noetherian ring. An acyclic complex $P$ of projective $R$-modules is called totally acyclic if for every projective $R$-module $Q$, the complex Hom$_R(P, Q)$ is also acyclic. …
Alex's user avatar
  • 480
6 votes
2 answers
292 views

If Serre's intersection multiplicity $\chi(R/I, R/J)$ equals $\operatorname{length}_R (R/(I+...

Let $(R,\mathfrak m)$ be a regular local ring. Let $I,J$ be proper ideals of $R$ such that $R/(I+J)$ has finite length i.e. $\sqrt{I+J}=\mathfrak m.$ Since $I+J$ annihilates $\text{Tor}_n^R(R/I, R/J)$ …
Alex's user avatar
  • 480
2 votes
1 answer
371 views

When is Hilbert-Samuel multiplicity of a local ring non-increasing along localization at pri...

For Noetherian local ring $(R,\mathfrak m)$, let $e(R)$ denote the Hilbert-Samuel multiplicity of $R$ with respect to $\mathfrak m$ (https://en.m.wikipedia.org/wiki/Hilbert%E2%80%93Samuel_function#Mul …
Alex's user avatar
  • 480
2 votes
0 answers
91 views

Minimal injective resolution and change of rings

Let $R$ be a commutative Noetherian ring. For an $R$-module $M$, let $0\to E^0_R(M)\to E^1_R(M)\to \ldots $ denote the minimal injective resolution of $M$. I have two questions: (1) If $I$ is an idea …
Alex's user avatar
  • 480
2 votes
1 answer
108 views

Example of non injective module over Noetherian local ring with trivial vanishing against re...

Is there an example of a module $M$ over a commutative Noetherian local ring $(R,\mathfrak m, k)$ such that $\text{Ext}_R^{>0}(k, M)=0$ but $M$ is not an injective $R$-module? I know that for such an …
Alex's user avatar
  • 480
1 vote
1 answer
81 views

Transcendence degree and Krull dimension for homomorphic images of power series rings

Let $k$ be a field of characteristic zero and $I$ be a radical ideal of $k[[x_1,\ldots, x_n]]$. Let $P$ be a minimal prime ideal of the reduced ring $R:=k[[x_1,\ldots, x_n]]/I$. Then, $R_P$ is a field …
Alex's user avatar
  • 480
1 vote
1 answer
89 views

On analytic transcendence degree and Krull dimension for homomorphic images of power series ...

Let $k$ be a field of characteristic zero and $I$ be a radical ideal of $k[[x_1,\ldots, x_n]]$. Let $P$ be a minimal prime ideal of the reduced ring $R:=k[[x_1,\ldots, x_n]]/I$. Then, $R_P$ is a field …
Alex's user avatar
  • 480