The mechanical computation of first and second cohomology groups
type: Item
instance of: scholarly article
title: The mechanical computation of first and second cohomology groups
zbMATH Open document ID: 0587.20035
DOI: 10.1016/S0747-7171(85)80020-1
published in: Journal of Symbolic Computation
publication date: 1985-01-01T00:00:00Z
review text: The author continues his work of ''A computer program for the calculation of the Schur multiplier of a permutation group'' [Computational group theory, Proc. Symp., Durham 1982, 307-319 (1984; Zbl 0544.20004); J. Pure Appl. Algebra 35, 287-295 (1985; Zbl 0552.20006)]. This paper describes the theory and implementation of algorithms to compute the dimension of the first and second cohomology groups. The input is (1) a finite group G given by generating permutations, and (2) matrices for the generators' action on a finite module M over \(K=GF(p)\), p prime. A combination of hand and mechanical calculation produces (3) a Sylow p- subgroup P of G, (4) a chain of subgroups \(P=H_ 0\leq H_ 1=N(P)\leq...\leq H_ n=G\), (5) suitable double coset representatives \(D_ i\) of \(H_{i-1}\) in \(H_ i\), \(i=1,2,...,n\), (6) \(P\cap P^ q\), \(P\cap P^{g^{-1}}\), for each g in the \(D_ i\) as further requirements of the algorithm. The algorithm uses variants of the nilpotent quotient algorithm to compute \(H^ x(P,M)\), and then computes \(H^ x(G,M)\) as the subgroup of stable elements of \(H^ x(P,M)\), \(x=1,2\). The author has a stand alone implementation written in C for the Unix operating system. Two examples - the natural 5-dimensional module of \(L_ 5(2)\), and a 6-dimensional module over GF(3) for \(L_ 3(9)\)- illustrate the performance of the program.
Mathematics Subject Classification ID: 20J06
Mathematics Subject Classification ID: 20C25
Mathematics Subject Classification ID: 20-04
Mathematics Subject Classification ID: 20F05
zbMATH DE Number: 3941803
zbMATH Keywords: implementation
zbMATH Keywords: algorithms
zbMATH Keywords: dimension of the first and second cohomology groups
zbMATH Keywords: generating permutations
zbMATH Keywords: Sylow p-subgroup
zbMATH Keywords: double coset representatives
zbMATH Keywords: nilpotent quotient algorithm
zbMATH Keywords: performance
author: Derek F. Holt
describes a project that uses: Cayley
MaRDI profile type: Publication
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description: scientific article; zbMATH DE number 3941803