> < ^ From:

> < ^ Subject:

On Thu, Jan 21, 1999 at 06:28:12PM +0100, Dmitrii Pasechnik wrote:

> Dear Forum,

>

> > I'm using version 4b5, and here's the problem I'm having:

>

> >gap> x:=Indeterminate(Rationals,"x");

> >x

> >gap> a:=AlgebraicExtension(Rationals,x^4-2*x^2+9);

> ><field in characteristic 0>

> >gap> RootOfDefiningPolynomial(a);

> >Error no method found for operation RootOfDefiningPolynomial at

> >[...]

>

> As far as I can see from the source code, this function is implemented

> so far for the finite fields only.

> This is easy to see by doing grep in <GAP-source-path>/gap4b5/lib/ :

>

> $ fgrep " RootOfDefiningPolynomial" *

> ffe.gi:#M RootOfDefiningPolynomial( <F> ) . . . . . . . for standard finite fields

> ffe.gi:InstallMethod( RootOfDefiningPolynomial,

> ffe.gi: return RootOfDefiningPolynomial( F );

> field.gd:#A RootOfDefiningPolynomial( <F> )

>

> (note that only the 1st line of the fgrep output is relevant in this case).

>

> As there is nothing w.r.t. "Polynomial" in

> <GAP-source-path>/gap4b5/src/, we can safely conclude that

> we haven't overlooked some other definition...

>

> Hope this helps,

> Dmitrii

Thanks for the response. Actually x^4-2*x^2+9 is a Galois Field, its

Galois closure group is C_2 x C_2. I wonder what's included in GAP's

definition of *standard finite fields*.

I'll double check at the GAP4 mailing list.

Igor

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