Dea Forum,
Tim Kohl asked
> On Dec 2, 2019, at 9:17 PM, tk...@math.bu.edu wrote:
>
>
> Dear forum members.
>
> In Maple, there are commands nops() and op() which allow
> one to 'pick apart' expressions, such as polynomials for example,
These Maple functions are the interface to Maples internal data type (which is
probably a tree structure for algebraic expressions).
>
> i.e. nops(expr) is the number of terms of expr
> op(1,expr) is the first term of expr
>
> although how nops() evaluates the number of terms is a bit subtle.
>
> Anyway, I was just wondering if GAP has similar commands?
GAP has similar commands (the most generic being ExtRepOfObject), though the
storage is different and thus interface routines are different.
>
> I am trying to sort (and pull apart) words in fp groups which are,
> of course, polynomials.
Probably you want LetterRepAssocWord. Note that the elements of fp groups wrap
words in the free group, thus one needs to call UnderlyingElement first:
gap> f:=FreeGroup("a","b");;
gap> g:=f/ParseRelators(f,"a2,b3,(ab)5");
<fp group on the generators [ a, b ]>
gap> s:=SylowSubgroup(g,2);;
gap> w:=GeneratorsOfGroup(s)[2];
b*a*b^-1*a*b*a^-1*b^-1*a^-1*b
gap> LetterRepAssocWord(UnderlyingElement(w));
[ 2, 1, -2, 1, 2, -1, -2, -1, 2 ]
Regards,
Alexander Hulpke
-- Colorado State University, Department of Mathematics,
Weber Building, 1874 Campus Delivery, Fort Collins, CO 80523-1874, USA
email: hul...@colostate.edu, Phone: ++1-970-4914288
http://www.math.colostate.edu/~hulpke
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