Questions tagged [homological-algebra]
(Co)chain complexes, abelian Categories, (pre)sheaves, (co)homology in various (possibly highly generalized) settings, spectra, derived functors, resolutions, spectral sequences, homotopy categories. Chain complexes in an abelian category form the heart of homological algebra.
2,708 questions
4
votes
0
answers
109
views
Higher cohomology groups of $\mathfrak{g}$-valued $1$-forms with values in $q$-forms
Consider the category of simplicial presheaves on the site of cartesian spaces (i.e., objects are open subsets of $\mathbb{R}^n$ that are diffeomorphic to $\mathbb{R}^n$ and morphisms are smooth maps. ...
- 928
2
votes
0
answers
84
views
Infinity-morphisms for operadic algebras
Is there an already studied notion of $\infty$-morphism between algebras over a quasi-free operad $P = (T(E), \partial)$?
If the operad $P$ is Koszul, or of the form $\Omega C$ for $C$ a cooperad, ...
- 215
2
votes
0
answers
104
views
$\mathrm{Tor}$'s for submodules of division rings
Let $R$ be a ring, $D$ a division $R$-ring in which $R$ embeds, and $M$ a finitely generated $R$-submodule of $D$. What, if anything, can be said about the finiteness properties of $M$? $\mathrm{Tor}^...
- 163
5
votes
0
answers
361
views
On a simple alternative correction to Roos' theorem on $\varprojlim^1$
Here is a discussion about an incorrect theorem of Roos, later corrected, some counterexamples and so on. Reading over this, I was a bit shocked because it contradicted something from Weibel's ...
- 1,021
3
votes
0
answers
79
views
Rational model for composition of linear isometries
There is a composition map on spaces of linear isometries (over $\mathbb{C}$ say)
$$
\mathcal{L}(\mathbb{C}^k, \mathbb{C}^\ell) \times \mathcal{L}(\mathbb{C}^\ell, \mathbb{C}^m) \longrightarrow \...
- 901
7
votes
0
answers
218
views
Twisting cochain intuition
I'm currently reading through Ed Brown's paper "Twisted tensor products, I", (MR105687, Zbl 0199.58201) and I couldn't find any simple examples of twisting cochains. I understand all ...
- 171
3
votes
1
answer
359
views
Is the adjunction between spaces and chain complexes monadic?
Consider the adjunction of $\infty$-categories $\mathbb{Z}[-]: \mathcal{Spaces} \rightleftarrows \text{Ch}_{\ge 0}(\mathbb{Z}): |-|$ where the left adjoint takes a space to its singular chain complex ...
- 423
2
votes
1
answer
112
views
Example of non injective module over Noetherian local ring with trivial vanishing against residue field?
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 ...
- 480
1
vote
0
answers
58
views
Which sheaves are good for calculating extraordinary restriction?
Let $X$ be a sufficiently nice locally compact Hausdorff space and let $i:Y\subset X$ be the inclusion map of a sufficiently nice closed subspace. For example, one could take $X$ to be a locally ...
- 23.5k
8
votes
1
answer
232
views
Product structure in Milnor exact sequence
Let $h^*$ be a (multiplicative) generalized cohomology theory. Let $X$ be a CW complex which is a union of an increasing sequence $X_0 \subset X_1 \subset X_2 \subset \cdots$ of subcomplexes. Then ...
- 959
2
votes
0
answers
93
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 ...
- 480
3
votes
2
answers
161
views
Is there a $ H_* H^* $-theory which is naturally a common generalization both of singular homology and de Rham (or singular) cohomology?
It is known that $K_* K^* $-theory is a common generalization both of $K$-homology and $K$-theory as an additive bivariant functor on separable C*-algebras.
Is it possible to construct a $ H_* H^* $-...
- 595
3
votes
1
answer
223
views
A morphism of double complexes induces a qis on total complexes under certain hypotheses. Proof involving a spectral sequence
$\def\Tot{\operatorname{Tot}}
\def\Ker{\operatorname{Ker}}$I am trying to understand the proof of Lemma 0133 of the Stacks Project. Note that hypotheses (3) and (4) can be restated by saying: extend ...
1
vote
0
answers
86
views
The derived exact couple of an exact couple without chasing elements
$\def\Ker{\operatorname{Ker}}
\def\Im{\operatorname{Im}}$Given an exact couple $(A,E,\alpha,f,g)$ in some abelian category, we define its derived exact couple $(A',E',\alpha',f',g')$ to be $A'=\alpha ...
1
vote
0
answers
80
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.
...
- 480
2
votes
0
answers
137
views
details of a dévissage argument for constructible sheaves
I am working on the following Künneth-type isomorphism from [SGA5, exposé III, 2,3]:
$\mathrm{Settings}.$ Let $X_1, X_2$ be separated finite type schemes over the spectrum of a field $S=\mathrm{Spec}...
- 375
0
votes
0
answers
90
views
Ding Gorenstein dimension
It is known that Gorenstein projective and Gorenstein injective dimensions of a ring R are equal. Is true also for ding projective and ding injective dimensions ?
- 11
3
votes
0
answers
130
views
Trace map on Ext group
Let $R$ be a (possibly non-commutative) unital ring and $M$ be a perfect left $R$-module. Then, we have the trace map
$$
\operatorname{Tr}\colon \mathrm{Hom}_R(M,M)\to R/[R,R]\,.
$$
According to the ...
- 985
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
3
votes
0
answers
69
views
Enriched tensor product of chain complexes
Question (idea): Is there a notion of tensor product of chain complexes in a $\mathcal{V}$-enriched monoidal category $\mathcal{C}$, for $\mathcal{V}$ a linear symmetric monoidal category?
Let me ...
- 213
7
votes
2
answers
313
views
How to get an $E_\infty$-ring from a commutative differential graded ring?
I want to figure out the following question: How to get an $E_\infty$-ring from a commutative differential graded ring?
More precisely, let $\operatorname{cdga}$ be the ($1$-)category of cdgas, let $...
- 81
4
votes
0
answers
238
views
Derived functors from localization vs animation
I got a bit confused with the derived functors getting from the localization and the animation. More specifically, let $\mathcal{A}$ be an abelian category generated by compact projective objects $\...
- 255
2
votes
0
answers
75
views
Sum of Betti numbers and certain short exact sequence of modules of finite length over regular local ring
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$ ...
- 480
2
votes
2
answers
416
views
Tensor product over $\mathbb{Z}$ and p-adic integer ring $\mathbb{Z}_p$
Thanks for your reading. Suppose we have two $\mathbb{Z}_p$-modules $A,B$. Do we always have $A \otimes_{\mathbb{Z}} B \simeq A \otimes_{\mathbb{Z}_p} B$, as abelian groups or $\mathbb{Z}_p$-modules? ...
- 319
6
votes
0
answers
126
views
Explicit proof that $\mathbb{k}[x]/(x^n)$ is not derived discrete
In the question Explicit proof that algebra is derived wild it was asked whether there are examples of algebras $A$ where it is possible to show explicitly that $A$ is derived wild by finding an ...
- 1,474
5
votes
1
answer
197
views
Examples of cyclic A-infinity algebra
I am wondering about (references to) examples of cyclic A-infinity algebras- especially including explicit descriptions of the structure maps and pairing.
Thanks a lot!
- 51
4
votes
0
answers
70
views
Explicit formula for Dold-Kan projection to normalized Moore complex
When proving the classical Dold–Kan correspondence (as e.g. in Goerss-Jardine book or here http://math.uchicago.edu/~amathew/doldkan.pdf), one associates three chain complexes to a simplicial abelian ...
- 66
5
votes
0
answers
288
views
Picard group of almost module category
I am very new to the world of almost mathematics and I am curious about the following:
Fix an almost mathematics situation $(R,I)$ throughout. Very generally, the almost module category comes with a ...
- 51
2
votes
1
answer
181
views
Is the derived support $\{x\in X\:|\: \mathsf{L}x^* M\neq 0\}$ closed?
Let $X$ be a scheme and consider an object $M$ of its derived category $\mathsf{D}_\text{qc}(X)$, defined as the full subcategory of $\mathsf{D}(\textsf{Mod}(\mathcal{O}_X))$ consisting of the ...
- 711
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$ ...
- 175
3
votes
0
answers
100
views
Pairing on a Koszul dual pair
Let $A$ be a graded quadratic algebra over a field $k$, and suppose that it admits the Koszul dual $A^!$. I want to know if there is a natural pairing $A\otimes A^!\to k$ or something similar to this. ...
- 985
2
votes
1
answer
210
views
Making a map in sheaf cohomology involving a theta characteristic explicit
Motivation:
For a given rank 2 vector bundle we want to know how many theta-characteristic valued twisted endomorphisms it has.
Setting:
Let $C$ be a smooth algebraic curve over a field of ...
3
votes
1
answer
172
views
1-1 map on the $\{0,1\}^k$
Let integer $k>0$ and let $\{0,1\}^k$ denote the set of all $1\times k$-dim vectors whose every coordinate is eithor 0 or 1, for example, $(0,1,1,0,\dots,1,0,0,1)$. For any such vector $\alpha$, ...
- 349
6
votes
1
answer
326
views
Spectral sequence generalizing Čech cohomology
Let $X$ be a 'nice' topological space. Let $\left(U_i\right)_{i\in I}$ be a finite open covering of $X$. Let $\mathcal{F}$ be a sheaf of abelian groups.
For a subset $A\subset I$ denote $$U_A:=\cap_{...
- 21.8k
4
votes
1
answer
267
views
A particular morphism being zero in the singularity category
Let $R$ be a commutative Noetherian ring and $D^b(R)$ be the bounded derived category of finitely generated $R$-modules. Let $D_{sg}(R)$ be the singularity category, which is the Verdier localization $...
- 361
3
votes
1
answer
152
views
Homotopy coherent transformation and totalization
Let $C$ be the category of chain complexes over a field $F$ and $C^\prime$ be the subcategory of chain complexes with zero differentials. If $X:I\to C$ is a functor, there is an induced "homology&...
- 410
3
votes
0
answers
40
views
Filtering a pre-Koszul algebra to get a homogeneous associated graded algebra
In Priddy's paper "Koszul resolutions", on p. 42 he defines an algebra $A$ to be pre-Koszul if it can be written as a quotient of a free algebra $F = F\langle x_i \rangle$ with generators $\{...
- 4,254
8
votes
1
answer
202
views
Integral homology of groups with finite exponent
I'm interested in the homology of infinite groups and especially in low-dimension integral homology.
If $G$ is a locally finite group of finite exponent, one has that also $H_*(G;\mathbb{Z})$ has ...
- 287
0
votes
0
answers
47
views
Generalized edge map in spectral sequence of double complex
suppose we have a cohomologically indexed double complex $C^{\bullet,\bullet}$ with its spectral sequence
$$E_2^{p,q}=H^p_{vert}(H^q_{horiz}(C))\Rightarrow H^{p+q}(C)$$
and suppose that the horizontal ...
- 2,044
2
votes
2
answers
126
views
Extensions of $G$-modules parametrized by $H^1$
Let $G$ be a finitely generated group and let $V$, $W$ be one-dimensional representations of $G$ over $\mathbb{F}_q$. (I guess one can think of $V$ and $W$ simply as $G$-modules, which are isomorphic ...
- 339
1
vote
0
answers
54
views
contravariant finiteness and limit closure: is there dual to a result of Crawley-Boevey?
Let $\mathcal A$ be a locally finitely presented category. Theorem 4.2 of https://doi.org/10.1080/00927879408824927 says that given a full additive subcategory $\mathcal D$ of finitely presented ...
- 480
3
votes
1
answer
164
views
Minimality of the Koszul resolution
Let $R = \mathbb{C}[x,y]$ and $V = \mathbb{C}x\oplus\mathbb{C}y$. Then, the Koszul resolution of $R$ (as an $R$-bimodule) is given by
\begin{align*}
0\to R\otimes_{\mathbb{C}}\wedge^2V\otimes_{\mathbb{...
- 985
0
votes
0
answers
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
1
answer
129
views
Thick subcategory containment in bounded derived category vs. singularity category
Let $R$ be a commutative Noetherian ring, and $D^b(\operatorname{mod } R)$ the bounded derived category of the abelian category of finitely generated $R$-modules. Let me abbreviate this as $D^b(R)$. ...
- 480
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
100
views
Koszul cohomology associated with a regular sequence
Let $A$ be a local Noetherian ring and $M$ be an $A$-module. Let $\mathfrak{a}$ be an ideal of $A$ generated by a regular $M$-sequence $s_1,\cdots,s_r$. Let $K_\bullet(s_1,\cdots,s_r;M)$ be the Koszul ...
- 439
27
votes
0
answers
468
views
Are these comparison morphisms between Čech and Grothendieck cohomology the same?
For better or for worse, there is more than one approach to comparing Čech cohomology $\smash{\check{H}}^\bullet(\mathfrak{U},X;\mathscr{F})$ of a sheaf $\mathscr{F}$ on a space $X$ w.r.t the cover $\...
- 1,021
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
311
views
Factoring through projective modules is an equivalence relation
$\DeclareMathOperator\Hom{Hom}\DeclareMathOperator\PHom{PHom}$I'm reading about stable module categories, and I have a question about the definition of the maps. Let $R$ be a ring, and take (left) ...
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 ...
- 26.5k