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This is a branch that includes: computational complexity theory; complexity classes, NP-completeness and other completeness concepts; oracle analogues of complexity classes; complexity-theoretic computational models; regular languages; context-free languages; Kolmogorov Complexity and so on.

8 votes

Groups whose word problem can be solved in constant time

This is a long comment rather than an answer. Using the ideas in the examples that you gave, you could show that any group that is virtually a direct product of finitely many free groups of finite ra …
Derek Holt's user avatar
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15 votes

Testing whether two elements of $\text{SL}(2, \mathbb{F}_{2^n})$ generate the entire group

The answer to your question is yes. The subgroups of ${\rm SL}(2,q)$ were classified by Dickson in 1901 (and probably earlier). For more general questions about subgroups of ${\rm GL}(n,q)$, there is …
Derek Holt's user avatar
  • 38.4k
10 votes
Accepted

Computing a transversal of a subgroup $H$ of $G$ in expected $O(|G : H|^2 \log |G : H| + |H|...

I guess I should try and answer that! I don't really have a good answer to the question of why the random method is not mentioned in the book, and I would agree that it might to be the fastest method …
Derek Holt's user avatar
  • 38.4k
6 votes
Accepted

Complexity of establishing finite groups (non)-isomorphism ?

It is unknown whether this problem is polynomial. It is at worst $O(N^{\log N})$. To see that, observe that the group can be generated by at most $\log N$ elements, a homomorphism is determined by the …
Derek Holt's user avatar
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20 votes
Accepted

Is the Normal centralizer problem in P?

Yes. This is Proposition 7.3 of Eugene M. Luks. Permutation groups and polynomial-time computation. Pages 139-175 of: Larry Finkelstein and William M. Kantor, editors. Groups and Computation, Volume …
Derek Holt's user avatar
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20 votes
Accepted

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

You seem to be asking for a description of the the algorithms in computational representation theory. I think that is far too broad a question for this site and you need to be more specific. There is …
Derek Holt's user avatar
  • 38.4k
6 votes
Accepted

Complexity of decision problem to decide if permutation group is $k$-transitive

There have been several articles on this forum discussing these topics, but here is a quick review. A base $B$ for a subgroup $G \le {\rm Sym}(X)$ is a sequence $(\alpha_1,\ldots,\alpha_k)$ of points …
Derek Holt's user avatar
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3 votes
Accepted

Complexity to decide for permutation group if every element fixed at most $k$ points

As I said in my comment, this problem is easily seen to be in P for fixed $k$, because we can compute all $(k+1)$-point stabilizers in polynomial time. So let's assume that $k$ is part of the input. …
Derek Holt's user avatar
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1 vote
Accepted

Algorithm to find a minimal normal subgroup of given group $G$ by matrix group representation

In the paper Holt, D., Leedham-Green, C. R., & O'Brien EA (2020). Constructing composition factors for a linear group in polynomial time. JOURNAL OF ALGEBRA, 561, 215-236. 10.1016/j.jalgebra.2020.02.0 …
Derek Holt's user avatar
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10 votes
Accepted

Time Complexity of the Word Problem for Finite Permutation Groups

As has been pointed out in comments, you cannot hope to do better in general than $O(n(l_1+l_2))$, where $n$ is the degree of the permutation groups and $l_1$, $l_2$ are the lengths of the words. But …
Derek Holt's user avatar
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29 votes
Accepted

Are there any computational problems in groups that are harder than P?

An earlier reference for groups with this property is J. Avenhaus and K. Madlener. Subrekursive Komplexität der Gruppen. I. Gruppen mit vorgeschriebenen Komplexität. Acta Infomat., 9 (1): 87-104, 197 …
Derek Holt's user avatar
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