From GAP-Forum-Sender@Math.RWTH-Aachen.DE Fri Feb 9 17:29 EST 1996
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Date: Fri, 09 Feb 96 23:03:00 +0100 (MET)
From: Martin Schoenert <martin.schoenert@math.rwth-aachen.de>
To: Multiple recipients of list <GAP-Forum@Math.RWTH-Aachen.DE>
Subject: Re: Shrink/ AbStab.g (reply)
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David Joyner wrote in his e-mail message of 1996/02/05

I hope I am not beating this poor AbStab.g horse/thread to death but I
still am having problems with the Shrink command which I cannot
resolve. I hope I am not wasting bandwidth but I would like to respond in
the hopes of clarifying the actual result which, to me, suggests that
Shrink might be the cause of the problem. (Though quite possibly I'm
wrong.)

'Shrink' is *definitely* not the cause of the problem. It does exactely

Martin:
I finally found the source of my error and you are absolutely right.
I thought the problem was in my maple code, so I ended up rewriting it
3 times, but that wasn't the problem. The problem was that some of
the generators were indexed wrong in my maple input file so even
though everything was correctly computed I misinterpreted the
output. Thanks again for the help. - David

what it should be doing. This can be seen as follows. If you define
r1,r2,r3,r4,f1,f2,...,f8 as in your e-mail message of 1996/01/31, and set

g1:=r4;; g2:=r3;; g3:=r2;; g4:=f4;; g5:=f3;; g6:=f2;; g7:=r1;;

and then evaluate the word found by 'Shrink':

g1^-2*g5^-1*g1*g4^-1*g1*g4^-1*g1^-1*g7^2*g5^-1*g1^-1*g5^-1*g7^-3
*g5^-1*g1^-1*g5^-1*g7*g5^-1*g1^2*g5^-1*g7*g5^-1*g1^-1*g5^-1*g7^-1
*g5^-1*g1^2*g5^-1*g7*g5^-1*g1^-1*g5^-1*g7^-1*g5^-1*g1^-4*g5^-1*g7
*g5^-1*g1*g5^-1*g7^-1*g5^-1*g1*g5^-1*g7^-2*g5^-1*g1^-1*g5^-1*g7*g5^-1
*g1^-1*g5^-1*g7^-1*g5^-1*g1^2*g5^-1*g7^4*g5^-1*g1*g5^-1*g7^-3*g5^-1
*g1^-1*g5^-1*g7*g5^-1*g1^2*g5^-1*g7^-1*g5^-1*g1*g5^-1*g7^3*g5^-1*g1
*g5^-1*g7^-3*g5^-1*g1^-1*g5^-1*g7^2*g5^-1*g1^-1*g5^-1*g7^-1*g5^-1;

You get the 2-cycle '(1,2)' (I just did it by cutting and pasting
everything into a GAP, and yes it worked). I also get '(1,2)'
when I evaluate the long word found by 'FactorPermGroupElement'.

If evaluating this word in Maple does not give '(1,2)' (or whatever
represents the 2-cycle in your Maple model), then there must be a
difference between the GAP and the Maple model.

Martin.

-- .- .-. - .. -.  .-.. --- ...- . ...  .- -. -. .. -.- .-
Martin Sch"onert,   Martin.Schoenert@Math.RWTH-Aachen.DE,   +49 241 804551
Lehrstuhl D f"ur Mathematik, Templergraben 64, RWTH, 52056 Aachen, Germany