All Questions
Tagged with rt.representation-theory homological-algebra
481 questions
2
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72
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Is a triangulated category admitting a tilting object triangle equivalent to the unbounded derived category of the endomorphism ring of this object?
Let $\mathcal{T}$ be a triangulated category. We call an object $G$ tilting if
$G$ is compact, that is, $\mathrm{Hom}_{\mathcal{T}}(G, -)$ preserves all set-indexed coproducts;
$G$ is a generator, ...
- 21
1
vote
1
answer
68
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An lower bound for the injective dimension of a module
Let $A$ be a finite dimensional algebra and $M$ a non-injective $A$-module.
Question: Do we have idim $M>$domdim $\tau^{-1}(M)$?
Here idim $N$ denotes the injective dimension of a module $N$ and ...
- 1,244
6
votes
3
answers
368
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Is there a finite dimensional algebra with left finitistic dimension different from its right finitistic dimension?
Let $\Lambda$ be finite dimensional algebra over a field $k$. The (left) finitistic dimension of a finite dimensional algebra is defined as
$$\operatorname{findim}(\Lambda)=\sup\{\operatorname{pd}M | ...
- 113
5
votes
2
answers
1k
views
An example where finitistic dimension does not equal right global dimension?
The (right) big finitistic dimension of a ring is Findim$(R) =$ sup{proj.dim(M) | $M$ a right $R$-module of finite projective dimension}. The (right) little finitistic dimension findim$(R)$ is the sup ...
- 113
1
vote
0
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80
views
Selforthogonal modules and finitistic dimension
Algebras $A$ are always finite dimensional over a field here.
A module $M$ is called selforthogonal if $\operatorname{Ext}_A^i(M,M)=0$ for all $i>0$.
Define the orthogonal finitistic dimension $\...
- 35.2k
3
votes
1
answer
301
views
If a bimodule is "generated" by single elements, must the elements be conjugate?
Let $A$ and $B$ be Artin $k$-algebras for a commutative artinian ring $k$ (e.g. $A$ and $B$ are finite dimensional $k$-algebras for a field $k$). Let $M$ be an $A$-$B$-bimodule of finite length over $...
- 696
3
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0
answers
107
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Dimension of hom spaces between indecomposable modules
Undergraduate-Level Background
Let $A$ be an Artin algebra over an algebraically closed field $k$, and let $C = Rep(A)$ denotes the category of $k$-linear, $k$-finite dimensional representations of $A$...
- 5,230
3
votes
1
answer
339
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If the Hom-space of finite length modules is generated by single elements, must the elements be conjugate?
Let $A$ be an Artin $k$-algebra for a commutative artinian ring $k$ (e.g. $A$ is a finite dimensional algebra over a field $k$). Let $X,Y$ be finite length left $A$-modules. If $\text{Hom}_A(X,Y)$ is ...
- 696
4
votes
1
answer
184
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FI-homology of a spectral sequence of rational FI-modules
Let $(E^r_{p,q})$ be a spectral sequence of rational $\mathsf{FI}$-modules. Call $H^{\mathsf{FI}}$ the $\mathsf{FI}$-homology (see here) and $t_k X= \deg H^{\text{FI}}_k X$ the $k$-th generation ...
- 3,948
16
votes
3
answers
1k
views
Conjectures in the representation theory of the symmetric group
Question: What are current open conjectures about the representation theory of the symmetric group?
I am interested mostly in the characteristic 0 case, but conjectures for the modular case can also ...
- 33.8k
4
votes
0
answers
75
views
Gluing the outer functors between two recollements
Assume there are two recollements of triangulated categories and the functors $f_1$ and $f_3$ below.
\begin{align*}
\begin{array}{rcccc}
{\mathbf{T}_1} & \underset{\underset{i_R}\leftarrow}{\...
- 41
4
votes
1
answer
101
views
Extension of scalars for bounded chain complexes of $kG$-modules
I'm wondering if a generalization regarding a statement from Curtis-Reiner holds. The original statement is as follows:
(30.33) Theorem: Let $R$ and $S$ be complete discrete valuation rings, with $S$ ...
- 16.2k
3
votes
1
answer
348
views
Finitistic dimension equal to cofinistic dimension for QF-3?
Given a finite dimensional algebra A such that the regular module embeds into a projective-injective module (such algebras are called QF-3 algebras and generalise Frobenius algebras).
Define the ...
CommunityBot
- 1
0
votes
0
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103
views
Matrix of the minimal projective presentation of a $\tau$-rigid module
Let $A$ be a finite dimensional algebra over an algebraically closed field $\mathbb{K}$ of characteristics zero. Suppose $A$ is given by the bound quiver $(Q,I)$. We will use $P_l$ to denote the ...
- 839
3
votes
0
answers
83
views
Connection between certain finite groups and Frobenius algebras
This question is maybe not so precise yet, but contains some ideas that maybe just search for the right definition.
Let $G=F/U$ be a finite group with presentation $F/U$ (here the presentation really ...
- 26.5k
2
votes
0
answers
45
views
$K_0$-basis modules with a unique extension related to parking functions
Let $B=B_n$ be the quiver algebra of type $A_n$ (with some orietnation) with $n$ points.
A $B$-module $M$ is a basis of the Grothendieck group $K_0$ if $M$ has $n$ indecomposable direct summands and ...
- 26.5k
6
votes
1
answer
197
views
Known posets of tilting modules for finite dimensional algebras
Question: For which classes of finite dimensional algebras $A$ is the poset of tilting $A$-modules known?
Here two famous examples:
-For the path algebra of a linear oriented quiver of Dynkin type $...
1
vote
0
answers
124
views
Computing the induced homomorphisms of derived functors using acyclic resolutions
Let's suppose that $F\colon \mathcal A\to \mathcal B$ is a right exact additive functor between abelian categories such that $\mathcal A$ has enough projectives. Standard references shows that if $Q_\...
- 38.6k
2
votes
0
answers
55
views
Depth and codepth of an algebra
Let $A$ be a finite dimensional $K$-algebra over a field $K$ and
$0 \rightarrow A \rightarrow I^0 \rightarrow I^1 \rightarrow \cdots$
a minimal injective coresolution of the regular module $A$.
The ...
- 26.5k
2
votes
2
answers
139
views
Infinite radical ideal cubed equals zero for tame hereditary Artin algebras
Let $A$ be a tame hereditary Artin algbera and mod$A$ the category of finitely generated (left) $A$-modules. Further, let rad$_A$ be the radical ideal of mod$A$, which is the smallest ideal containing ...
- 216
2
votes
0
answers
67
views
Bounds for sum of the homological dimensions in the incidence algebra of a Boolean lattice
Let $A$ be a finite dimensional algebra.
Define $\varphi_A:= \sup \{ \operatorname{pd} M + \operatorname{id} M \mid M \in \operatorname{ind}(A) \}$, where $\operatorname{pd} M$ denotes the projective ...
4
votes
1
answer
198
views
Does hereditary and connected imply that the underlying ring $k$ of a $k$-algebra is a field?
All rings are assumed to be associative and have a 1. Let $k$ be a commutative artininan ring and $R$ a finitely generated $k$-algebra. Is it true that if $R$ is connected and hereditary, then $k$ is ...
CommunityBot
- 1
6
votes
1
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310
views
A formula for the projective dimension of finite dimensional algebras
Let $A$ be a finite dimensional ring-indecomposable $K$-algebra that is not selfinjective for $K$ a field and let $I(A)$ denote the injective envelope of the regular module $A_A$. Define the stable $A$...
- 35.2k
2
votes
1
answer
173
views
Using the mapping cone to show that a chain map defines a stable equivalence between two symmetric algebras
This question is about an argument in the proof of Theorem 9.8.8 in Linckelmanns Block Theory of Finite Group Algebras. I need to understand the argument in order to do something similar in my ...
- 35.2k
4
votes
1
answer
302
views
Hattori-Stallings trace
Let $R$ be a (possibly non-commutative) unital ring and $M$ be a left $R$-module. If $M$ is finitely generated and projective, the natural map $$\iota:\mathrm{Hom}_R(M,R)\otimes_R M\to \mathrm{Hom}_R(...
5
votes
0
answers
213
views
Rings where all indecomposable modules are projective or injective
Let $A$ be a semi-perfect noetherian ring.
Is there a nice classification of such $A$ such that every indecomposable finitely generated $A$-module is projective or injective?
Im also interested in ...
- 26.5k
8
votes
1
answer
534
views
Representation theory of $\mathrm{GL}_n(\mathbb{Z})$
I want to understand the (complex) representation theory of $\mathrm{GL}_n(\mathbb{Z})$, the general linear group of the integers. I have gone through several representation theory texts but all of ...
- 63.9k
3
votes
0
answers
104
views
A depth version of a conjecture of Yamagata
Let $A$ be a finite-dimensional $K$-algebra.
Recall that the grade of an $A$-module $M$ is defined as the smallest $i$ such that $\operatorname{Ext}_A^i(M,A) \neq 0$ and the depth of $A$ is defined ...
- 35.2k
6
votes
0
answers
178
views
Ext for commutative Gorenstein algebras
Let $A$ be a finite dimensional commutative Gorenstein $K$-algebra over a field $K$.
Question 1: Is there an easy example of $A$-modules $M$ and $N$ such that $\mathrm{Ext}_A^1(M,N)=0$ but $\mathrm{...
- 1,313
8
votes
2
answers
960
views
Is the derived category of local systems equivalent to the derived category of sheaves of vector spaces with local system cohomology?
Let $k$ be a field and $X$ a topological space.
Write $\mathrm{Sh}(X)$ for the category of sheaves of vector spaces on $X$, and $\mathrm{Loc}(X)$ for the subcategory of local systems of finite ...
- 1,071
1
vote
0
answers
106
views
Uniqueness of indecomposable decomposition (Krull–Schmidt) for finitely generated modules over commutative Noetherian standard graded rings
Let $R_0=\mathbb C$ and $R=\bigoplus_{i\geq 0} R_i$ be a commutative Noetherian graded ring such that the grading is standard, i.e., $R=R_0[R_1]$. Let $M$ be a finitely generated $R$-module. Evidently,...
- 412
2
votes
1
answer
184
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Gorenstein projective module over commutative local algebras
Let $A$ be a local commutative finite dimensional algebra over a field $K$.
An $A$-module $M$ is called Gorenstein projective if $M$ is reflexive, $Ext_A^i(M,A)=0=Ext_A^i(M^{*},A)$ for all $i>0$ ...
- 642
8
votes
1
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356
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Homological conjectures for finite dimensional commutative algebras
$\DeclareMathOperator\Ext{Ext}\DeclareMathOperator\Hom{Hom}$>Question: What are some (open) homological conjectures that are also relevent for finite dimensional commutative algebras over a field $...
- 16.2k
3
votes
1
answer
129
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Extensions for simple modules over group algebras
Let $G$ be a finite group and $K$ a field with field extension $L$ ($K$ perfect and $L$ finite field extension first for simplicity),
Let $S$ be a simple $KG$ module.
Viewed as a $LG$-module $S$ ...
- 16.2k
14
votes
1
answer
835
views
Special configurations on a circle from a homological algebra problem
Here is the short version of the combinatorial problem:
Given a positive integer $n \geq 2$. Draw a circle with $2n$ points indexed by the numbers from $\mathbb{Z}/ 2n \mathbb{Z}$. We colour the ...
- 34.3k
2
votes
0
answers
86
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Example of a triangular string algebra that is rep infinite, but $\tau$-tilting finite
Let $A$ be a finite dimensional algebra over an algebraically closed field $\mathbb{K}$. Hence, $A$ can be realized as the path algebra of a bound quiver $(Q,I)$, where $I\subseteq\mathbb{K}Q$ is an ...
- 839
2
votes
1
answer
165
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Rep infinite, but $\tau$-tilting finite
Let $A$ be a finite dimensional algebra over an algebraically closed field. I'm trying to better understand the difference between $A$ being representation infinite and $A$ being $\tau$-tilting ...
- 839
7
votes
1
answer
287
views
Semi-projective complexes of modules over a finite group
Let $G$ be a finite group and $k$ a field of characteristic $p$ dividing $|G|$. A perfect complex of $kG$-modules is by definition a finite complex of finitely generated projective ($=$ injective $=$ ...
- 35.2k
2
votes
0
answers
77
views
Equivalence of two descriptions of differentials of Koszul complex
My question comes from learning the paper [BGS96] Koszul duality patterns in representation theory by Beilinson, Ginzburg and Soergel, published in 1996.
Let $A=T_{A_0}A_1/\langle R\rangle$ be a ...
- 21
3
votes
0
answers
73
views
Turning a Frobenius algebra into a symmetric algebra via tensor products
Let $A$ be a finite dimensional Frobenius algebra over a field $K$, which means that $A \cong D(A)$ as right $A$-modules. Being symmetric means that $A \cong D(A)$ as $A$-bimodules. Here $D(-)=Hom_K(-,...
- 26.5k
3
votes
0
answers
85
views
Exterior powers of the Cartan matrix and Dyck paths
(This question can be formulated purely combinatorially in terms of Dyck paths, which is done in the second part of the question. But I am more interested whether this can be explained by some sort of ...
- 26.5k
4
votes
2
answers
771
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Finitistic dimension conjecture for quadratic algebras
The finitistic dimension of a finite dimensional algebra is defined as the supremum of all projective dimensions of modules having finite projective dimension. The finitistic dimension conjecture says ...
28
votes
4
answers
3k
views
Yoga of six functors for group representations?
I'm trying to understand how the six functor philosophy applies to representation theory. Consider the category of classifying stacks $BG$ (assume $G$ discrete for simplicity). To every stack we can ...
- 21.3k
3
votes
1
answer
173
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$\Omega$ for noetherian semiperfect rings
Let $A$ be a a two-sided noetherian semiperfect ring and assume that the injective dimension of the left and right regular modules are equal to $n \geq 1$.
Let $\Omega^n(mod A)$ be the category of $n$-...
- 16.2k
3
votes
1
answer
187
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Explicit proof that algebra is derived wild
Following the terminology of
Drozd, Yuriy A., Derived tame and derived wild algebras, Algebra Discrete Math. 2004, No. 1, 57-74 (2004). ZBL1067.16028.
let $A$ and $R$ be algebras over a field $k$. A ...
- 497
3
votes
1
answer
149
views
Bounds for the number of edges in an Alperin diagram
If $A$ is an algebra over a field $k$ and $M$ is a finite-dimensional $A$-module, then Alperin showed in a paper [Diagrams for modules, JPAA, 1980] how to associate a diagram to $M$ with the vertices ...
CommunityBot
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1
vote
0
answers
52
views
Is the Schofield semi invariant defined at $V/IV$?
Let $A=\mathbb{K}Q$ be the path algebra of an acyclic quiver $Q$ over an algebraically closed field $\mathbb{K}$, and $0\not=I\subset\mathbb{K}Q$ be an admissible ideal. Let $W$ be a left $A$-module ...
- 839
6
votes
2
answers
229
views
Bounding the projective dimension of modules by the number of points and arrows
Let $A=KQ/I$ be a finite dimensional connected quiver algebra with admissible ideal $I$ with n points and m arrows and $M$ an $A$-module.
Question: Is the projective dimension of $M$ bounded by $n+m$ ...
- 4,713
2
votes
0
answers
138
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Construction of a certain long exact sequence
Let $A$ be a noetherian ring (not necessarily commutative) or for simplicity even a finite dimensional algebra over a field.
Let $X$ and $U$ be finitely generated $A$-modules and let $add(U)$ be the ...
- 26.5k
4
votes
1
answer
107
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For a finite dimensional $k$-Algebra $A$ does infinite representation type imply $(\text{rad}_A^{\omega})^2 \neq 0$?
Let $k$ be a field, $A$ a finite dimensional $k$-Algebra, $\text{mod}\,A$ the category of finite dimensional left $A$-modules and $\text{rad}_A$ the collection of radical morphisms in $\text{mod}\,A$. ...
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