All Questions
Tagged with rt.representation-theory ra.rings-and-algebras
424 questions
4
votes
1
answer
141
views
Kernels of actions on truncated polynomial algebra
Let $p$ be an odd prime, and let $k=\mathbb{F}_p$ be the field with $p$ elements. Let $G=\text{GL}_n(k)$. The group $G$ acts on the truncated polynomial algebra $A:=k[x_1,\ldots, x_n]/(x_1^p,\ldots, ...
- 5,039
3
votes
1
answer
173
views
$\Omega$ 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 $n$-...
- 26.5k
1
vote
0
answers
78
views
tensor dimension/reshaping group
Consider an $N$ dimensional tensor $T$ using the strided view representation used by PyTorch, i.e. we have a storage vector $S$ projected into $N$ dimensions using a size tuple $s$ and a stride tuple $...
- 11
4
votes
1
answer
296
views
Classification of simple modules for the free algebra
Let $A=K\langle x,y\rangle$ be the free associative algebra in two generators over a field $K$ (we can assume that the field is algebraically closed or even $K=\mathbb{C}$ first if that helps)
...
- 26.5k
2
votes
1
answer
107
views
Proof of restrictableness of Lie algebra without basis
$\DeclareMathOperator\ad{ad}$According to the Strade and Farnsteiners' textbook, a Lie algebra $L$ is restrictable if and only if $\ad(L)$ is $p$-subalgebra of $\operatorname{Der}(L)$. Also, the ...
- 145
3
votes
1
answer
382
views
What is the name for algebras generated by elements, all of whose cubes vanish?
Given a ring $R$ with identity $1$, we can define the exterior algebra of order $k$ over $R$ to be the algebra over $R$, generated by elements $x_1, \dots, x_k$ satisfying $x_i^2 = 0$ for each index $...
- 557
2
votes
0
answers
138
views
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
2
votes
0
answers
98
views
Question concerning relationships between different $p$-modular systems and Brauer character values
Let $(K,\mathcal{O},k)$ be a large enough $p$-modular system, where $\mathcal{O}$ is a complete discrete valuation ring of characteristic zero with unique maximal ideal $J(\mathcal{O})$, algebraically ...
- 1,755
1
vote
0
answers
81
views
Structure and representation of a non-homogeneous quadratic algebra
Let $m$ be a positive integer and $s$ be a fixed $m\times m$ matrix. Let $U$ be the unital associative algebra (over $\mathbb{C}$) generated by $\{u^i_{j}\}_{1\leq i,j\leq m}$ quotient over the ...
- 727
4
votes
1
answer
273
views
Wedderburn decomposition of special linear groups
$\DeclareMathOperator\SL{SL}\newcommand\card[1]{\lvert#1\rvert}$I want to study about Wedderburn decomposition of group algebra $k\SL(n,\mathbb{F}_p)$ where $k$ is either an algebraically closed field ...
- 249
5
votes
1
answer
393
views
Simple component that is not a two-sided ideal
Suppose $R$ is a semisimple ring and if $L$ is a minimal left ideal. Let $B$ be the direct sum of all minimal left ideals isomorphic to $L$ ($B$ is called a simple component corresponding to $L$). It ...
- 249
1
vote
0
answers
128
views
Example of a brick-infinite, tame, triangular algebra of global dimension$\geq 3$
I'm trying to compute some examples and I'm unable to come up with a following example:
What is(are) the example(s) of an acyclic quiver $Q$ with relations such that the 2-Kronecker quiver is NOT a ...
- 839
1
vote
0
answers
115
views
Prove that $B$ is a directing module
Let $A\cong\mathbb{K}Q/I$ be a finite dimensional, associative, basic $\mathbb{K}$ algebra, where $\mathbb{K}$ is algebraically closed and $Q$ is a finite Gabriel quiver on $n$ vertices and $I\...
- 839
3
votes
1
answer
106
views
Reference request for equivalent formulations of being absolutely indecomposable
I would like to ask the following question.
I am searching for a reference for the following statement:
Suppose $k$ is a perfect field. Let $A$ be a (symmetric) $k$-algebra and let $M$ be a finitely ...
- 311
5
votes
1
answer
400
views
Injective modules
Let $A$ be a finite dimensional $k$-algebra and let $I$ be an injective module。My question is whether $I$ is a direct sum of finite-dimensional injective modules。
- 169
2
votes
0
answers
268
views
Understanding a proof of a result of Schofield
I'm reading a paper of Aidan Schofield- "General Representations of Quivers" and I'm trying to understand the proof of Theorem 3.3. I'm having trouble understanding the argument that's ...
- 839
2
votes
0
answers
92
views
Is there a standard reference for: taking projective covers of simple modules commutes with finite Galois field extensions?
Let $\Lambda$ be an Artin algebra over a finite field $k$. Is there a standard reference for the fact that taking projective covers of simple $\Lambda$-modules commutes with finite Galois field ...
- 311
1
vote
1
answer
218
views
A result of Schofield in the case of quivers with relations
Let $Q$ be a quiver without oriented cycles. A result of Schofield says that, for dimension vectors $\alpha$ and $\beta$ of $Q$, $\beta\hookrightarrow\alpha$ iff $\operatorname{ext}(\beta, \alpha-\...
- 839
15
votes
1
answer
639
views
What is the centralizer of a Young subgroup of $S_n$?
In their celebrated paper "A new approach to the representation theory of the symmetric group. II", Okounkov and Vershik prove that $Z(n-1,1)$, the centralizer of $\mathbb{C}[S_{n-1}]$ in $\...
- 492
7
votes
1
answer
284
views
Does the choice of the algebraically closed field of characteristic $p$ have influence on the module category?
Let $G$ be a finite group and $p$ be a prime number dividing $|G|$.
Let $k$ be the algebraic closure of $\mathbb{F}_p$.
Let $K$ be another algebraically closed field of characteristic $p$ which is not ...
- 237
3
votes
1
answer
116
views
Dimension of division rings coming from indecomposable modules
Let $k$ be a field, $A$ a $k$-algebra and $X$ a finite dimensional indecomposable $A$-module. Then $\text{End}_A (X)$ is a local ring. Let $m$ be its maximal ideal. Can we say anything about the $k$-...
- 696
5
votes
1
answer
103
views
Classification of representation-finite hereditary rings
It is well known that one can associate to a finite dimensional hereditary algebra $A$ a diagram $G(A)$ and then show that $A$ is representation-finite if and only if $G(A)$ is a disjoint union of the ...
- 26.5k
3
votes
1
answer
171
views
Modules with special properties
$\DeclareMathOperator\End{End}$Let $A$ be a finite dimensional algebra and $M$ an indecomposable (right) module with the property that every nilpotent element of $\End_A(M)$ annihilates the socle $\...
- 26.5k
3
votes
0
answers
317
views
How to go from primitive idempotents in $\text{End}_A(M)$ to primitive idempotents in $A$?
Let $K$ be a large enough finite field, let $A$ be a finite-dimensional $K$-algebra.
Moreover, let $M$ be a finitely generated $A$-module and let $M = M_1\oplus ... \oplus M_n$ be a decomposition of $...
- 1,755
8
votes
2
answers
225
views
Lifting isomorphisms between linear categories
Let $C$ be a $\mathbb{Z}$-linear category, such that $C(x,y)$ is a free abelian group with finite rank, for every $x,y\in\mathrm
{Ob}(C)$. Given a commutative ring with identity $R$, let $RC$ denote ...
- 245
3
votes
0
answers
86
views
Terminology question
Let $K$ be a commutative ring with unit and suppose that $R$ is a ring that is a left $K$-module satisfying $c(rs)=(cr)s$ for all $c\in K$ and $r,s\in R$. We do not require that $r(cs)=c(rs)$ and so $...
- 38.6k
2
votes
1
answer
257
views
Possible "algebraic" direction in hyperplane arrangements
I have been studying hyperplane arrangements from R. Stanley's notes and so far, I have read until lecture 5. But, Lecture 6 and end of Lecture 5 seems very combinatorial. I'm more interested in the &...
- 839
3
votes
1
answer
158
views
Local Frobenius algebras and their opposite algebras
Assume all algebras are finite dimensional quiver algebras over a field (no restriction of generaltiy if the field is algebraically closed).
Let A be a local Frobenius algebra.
Is A isomorphic to its ...
- 26.5k
14
votes
2
answers
741
views
Is a "separable" algebra over a field finite-dimensional?
Let $k$ be a field and $A$ a unital associative (possibly non-commutative) $k$-algebra, and let $A^e$ denote the enveloping algebra of $A$, namely, $A^e = A \otimes_k A^{op}$.
It seems that there are ...
- 149
5
votes
1
answer
713
views
Absolutely irreducible representation and splitting field
Let $A$ be a finite-dimensional algebra over a field $F$. A representation $M$ of $A$ is called absolutely irreducible if $M\otimes_FE$ is irreducible as a representation of $A\otimes_FE$ for all ...
- 951
5
votes
0
answers
108
views
Indecomposable objects in iterated functor categories
Let $\mathcal{O}$ be a DVR with a uniformizer $\pi$ and a finite quotient field $\mathbb{F}_q=\mathcal{O}/\pi$. Write $\mathcal{O}_r = \mathcal{O}/(\pi^r)$. Fix now an integer $r\geq 2$. We define ...
- 5,039
1
vote
1
answer
190
views
Commutative subalgebra of Iwahori-Hecke algebra
I am currently reading the (french) book [1] by Matsumoto. In (2.1.11) the following statement (reformulated in my own words/notation) appears:
Let $(W,S)$ be a Coxeter system, let $R$ be a ...
- 741
7
votes
1
answer
281
views
Question concerning the coefficients of block idempotents
Let $G$ be a finite group. Let $p$ be a prime number such that $p \mid |G|$.
Let Irr$(G)$ denote the set of ordinary irreducible characters of $G$.
For $\chi\in$ Irr$(G)$ define $e_{\chi} := \frac{\...
- 1,755
2
votes
0
answers
55
views
Quiver algebras whose modules have a distributive submodule lattice
Is there a classification (by quiver and relations) of finite dimensional quiver algebras such that every indecomposable right module has a distributive submodule lattice?
- 26.5k
6
votes
1
answer
630
views
Representation ring of the symmetric group $S_n$ in the limit as $n \to \infty$
Let $S_n$ denote the symmetric group on $n$-letters and let $\mathrm{Rep}(S_n)$ denote its representation ring. For every $n$ restriction along the inclusion $S_{n-1} \to S_n$ induces a ring ...
- 7,789
3
votes
1
answer
162
views
Auslander-Reiten quiver of quiver algebra kQ where Q is of extended dynkin type D4~
I am looking for literature about the Auslander-Reiten quiver of the quiver algebra $kQ$, where $Q$ is of extended dynkin type $\tilde{D_4}$ and $k$ is an algebraically closed field. Does somebody ...
- 696
9
votes
2
answers
2k
views
A ring for which the category of left and right modules are distinct
What is an example of a ring $R$ for which the abelian category of left $R$-modules is not isomorphic to the category of right $R$-modules?
- 435
4
votes
2
answers
299
views
Relation of the first Hochschild cohomology and the outer automorphism group
Let $R$ be a ring.
Qeustion: Is it true that the first Hochschild cohomology of $R$ is zero if and only if the outer automorphism group of $R$ is finite?
(It is not true, by the two answers. Is it ...
- 26.5k
2
votes
0
answers
92
views
Expressing elements in Verlinde ideal in terms of generators
It is known that the level $k$ Verlinde ring of $SU(n)$ is $R(SU(n))/I_k$, where $I_k$ is the Verlinde ideal. A set of generators of $I_k$ is given by $\{V_{(k+i)L_1}:=\text{Sym}^{k+i}V_{\text{std}}| ...
- 383
2
votes
0
answers
141
views
Actions of rings (and other algebraic structures) on abelian categories
On the project I am currently working on, there are abelian, Krull-Schmidt categories $\mathcal{C}$ where it seems natural to equip $\mathcal{C}$ with the action of a ring $R$ (in some cases a ...
- 482
6
votes
1
answer
255
views
A weight generalization of root systems?
For any simple complex Lie algebra $\frak{g}$, with a given choice of Cartan subalgebra $\frak{h}$, we have an associated root system $R \subseteq \frak{h}^*$. The properties of $R$ can be formalized ...
- 123
10
votes
1
answer
272
views
Plane partitions as irreducible representations
The irreducible representations of the symmetric group algebras $A_n=KS_n$ over a the complex numbers (or any field of characteristic 0) $K$ satisfy the following properties:
The irreducible ...
- 26.5k
2
votes
0
answers
82
views
Minimizing the spectral radius of certain elements of group rings
Let $G$ be a finite group. Let $I_{G}$ be the ideal on the group ring $\mathbb{C}[G]$ consisting of elements of the form $\alpha\cdot\sum_{g\in G}g$.
Let $\lambda_{n}(G)$ be the minimum spectral ...
6
votes
1
answer
244
views
What is a Serre-smooth algebra?
Let $A$ be an $R$-algebra.
In the book "Noncommutative Geometry and Cayley-smooth Orders" by Le Bruyn one can find the notion of "Serre-smooth" in the introduction.
But no formal ...
- 26.5k
5
votes
2
answers
357
views
Is this quiver with relations of finite representation type
Let $Q=(Q_0,Q_1)$ be the following quiver, $Q_0$ consist of 2 vertices, denoted by 1,2. $Q_1$ consist a loop at 1 called $\gamma$, an arrow $\alpha$ from 1 to 2 and an arrow $\beta$ from 2 to 1. The ...
- 775
1
vote
0
answers
92
views
The $U({\frak g})v$-module generated by a single element of a $U({\frak g})v$-module
Let $\frak{g}$ be a finite dimensional complex semisimple Lie algebra and let $U(\frak{g})$ be its universal enveloping algebra. Take $V$ an infinite dimensional module over $U(\frak{g})$. Let $v \in ...
8
votes
1
answer
198
views
Is there always a simple module whose Green correspondent is a simple module under some conditions?
Let $G$ be a finite group and $KG$ its group algebra over some field $K$ with $\mathrm{char}\ K$ dividing the order of $G$. It's well-known that the Green correspondence is compatible with the Brauer ...
- 775
14
votes
4
answers
2k
views
A finite dimensional algebra associated to the symmetric group
Let $S_n$ be the finite group given as $n \times n$ permutation matrices.
Define for a given field $K$ the algebra $B_n$ as the subalgebra of $M_n(K)$ generated by all permutation matrices of $S_n$. (...
- 26.5k
2
votes
1
answer
124
views
When is a hypersurface in a quasi-polynomial ring finite dimensional?
$\newcommand\la{\langle}\newcommand\ra{\rangle}\newcommand\laa{\langle\!\langle}\newcommand\raa{\rangle\!\rangle}$
Assume in the following that every polynomials is a sum of monomials of degree at ...
- 26.5k
11
votes
1
answer
329
views
Are there three non-commutative polynomials in three variables with finite dimensional quotient?
$\newcommand\la{\langle}\newcommand\ra{\rangle}$Let $K$ be a field and $K\la x,y,z\ra$ the non-commutative polynomial ring in 3 variables.
Question 1: Are there three (fewer is probably not possible?!...
- 26.5k