Introductory computations in the cohomology of arithmetic groups

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Auteur principal: Ellis, Graham
Format: Preprint
Publié: 2020
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author Ellis, Graham
author_facet Ellis, Graham
contents This paper describes an approach to computer aided calculations in the cohomology of arithmetic groups. It complements existing literature on the topic by emphasizing homotopies and perturbation techniques, rather than cellular subdivision, as the tools for implementing on a computer topological constructions that fail to preserve cellular structures Furthermore, it focuses on calculating integral cohomology rather than just rational cohomology or cohomology at large primes. In particular, the paper describes and fully implements algorithms for computing Hecke operators on the integral cuspidal cohomology of congruence subgroups $Γ$ of $SL_2(\mathbb Z)$, and then partially implements versions of the algorithms for the special linear group $SL_2({\cal O}_d)$ over various rings of quadratic integers ${\cal O}_d$. The approach is also relevant for computations on congruence subgroups of $SL_m({\cal O}_d)$, $m\ge 2$.
format Preprint
id arxiv_https___arxiv_org_abs_2009_00313
institution arXiv
publishDate 2020
record_format arxiv
spellingShingle Introductory computations in the cohomology of arithmetic groups
Ellis, Graham
Number Theory
K-Theory and Homology
11F75
This paper describes an approach to computer aided calculations in the cohomology of arithmetic groups. It complements existing literature on the topic by emphasizing homotopies and perturbation techniques, rather than cellular subdivision, as the tools for implementing on a computer topological constructions that fail to preserve cellular structures Furthermore, it focuses on calculating integral cohomology rather than just rational cohomology or cohomology at large primes. In particular, the paper describes and fully implements algorithms for computing Hecke operators on the integral cuspidal cohomology of congruence subgroups $Γ$ of $SL_2(\mathbb Z)$, and then partially implements versions of the algorithms for the special linear group $SL_2({\cal O}_d)$ over various rings of quadratic integers ${\cal O}_d$. The approach is also relevant for computations on congruence subgroups of $SL_m({\cal O}_d)$, $m\ge 2$.
title Introductory computations in the cohomology of arithmetic groups
topic Number Theory
K-Theory and Homology
11F75
url https://arxiv.org/abs/2009.00313