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Questions on group theory which concern finite groups.

9 votes
2 answers
155 views

Coboundary matrix of bar resolution for group cohomology: do the elementary divisors always ...

Consider the coboundary matrix $C^1(G, \mathbb{Z}) \to C^2(G, \mathbb{Z})$ of the normalized bar resolution of $G$ with coefficients in the trivial $\mathbb{Z}G$-module $\mathbb{Z}$. That is, thinking …
Joshua Grochow's user avatar
4 votes

Smallest $n$ for which $G$ embeds in $S_n$?

There has been some recent progress on algorithms for this problem. Das & Thakkar STOC '24 give the following algorithms: For groups with no abelian normal subgroups, given by a generating set of per …
Joshua Grochow's user avatar
5 votes

Complexity of establishing finite groups (non)-isomorphism ?

I agree w/ Holt's technical statements (not sure whether I agree about his guess on the final running time, though I agree about which groups are likely to be hardest). But I wanted to add that a lot …
Joshua Grochow's user avatar
5 votes
1 answer
242 views

Local vs global nilpotence class (Lazard correspondence)

The Lazard Correspondence is often phrased (for simplicity) for $p$-groups of nilpotence class $c < p$, but it works more generally whenever every 3-generated subgroup has nilpotence class $< p$, and …
Joshua Grochow's user avatar
26 votes
2 answers
1k views

Is the cohomology ring of a finite group computable?

Is there an algorithm which halts on all inputs that takes as input a finite group ($p$-group if you like) and outputs a finite presentation of the cohomology ring (with trivial coefficients $\m …
Joshua Grochow's user avatar
17 votes
Accepted

In what sense is the classification of all finite groups "impossible"?

One can make the argument by wildness much more concrete than in the previous answer: Sergeichuk ["Classification of metabelian p-groups", in: Matrix problems, Inst. Mat. Ukrain. Akad. Nauk, Kiev, 19 …
Joshua Grochow's user avatar
3 votes

Is the classification of finite p-groups a smooth problem?

1) The classification of p-groups (even p-groups of class 2) is indeed wild over $\mathbb{F}_p$ [V. Sergeichuk, The classification of metabelian p-groups (Russian), Matrix problems, Akad. Nauk Ukrain. …
Joshua Grochow's user avatar
9 votes

How to compute all irreducible representations of a finite group ? (how GAP is doing this?)

If the group is given by its multiplication table then there are polynomial-time algorithms for all the tasks you mentioned (over $\mathbb{C}$; these don't handle modular representations). Babai and …
Joshua Grochow's user avatar