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Dear Radu Murgescu,

I am trying to compute the automorphism groups of some infinite groups

(free groups of small rank, in particular), but the AutomorphismGroup

function doesn't seem to work (I get an error message). Does the

argument to this function have to be a finite object? Any suggestions

of how I should deal with this would be appreciated.

as far as I know, at present GAP does not provide any algorithms for

computing automorphism groups of infinite groups. (The error message

you get is probably a "no method found" error, which indicates this).

However, the automorphism group of a free group of finite rank is

well-known. You can find explicit finite presentations (with usually

four or two generators, respectively) of these automorphism groups in

papers by Nielsen (Math. Ann. 91 (1924), 169-209) and B. H. Neumann

(Math. Ann. 107 (1932), 367-386). A student here is presently looking

at an implementation in GAP.

Please note that it depends very much on the type of questions you

have whether you can compute the answer with these finite

presentations (of infinite groups) in GAP.

Best regards,

Burkhard Höfling. -- _________________________________________________________________ Dr. Burkhard Höfling Phone (0531) 391 7526 Institut für Geometrie Phone intl. +49 531 391 7526 Technische Universität Fax (0531) 391 8210 Pockelsstr. 14 Fax intl. +49 531 391 8210 38106 Braunschweig, Germany WWW www.tu-bs.de/~bhoeflin

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