Bill Allombert on Fri, 31 Jan 2003 15:06:58 +0100

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Re: ffinit

On Fri, Jan 31, 2003 at 02:00:06PM +0000, Cherry Kearton wrote:
> I want to work with finite fields, and in the PARI manual it says that 
> ffinit is designed for this.  Specifically it says "For instance if P = 
> ffinit(3,2,y), you can represent elements in F3 2 as polmods modulo P." 
>  But if one sets
> a=Mod(1,P)
> then
> a+a+a=Mod(3,P),
> whereas I would expect Mod(0,P).
> How is one supposed to deal with finite fields under GP?

You need to write

? a+a+a
%9 = Mod(Mod(0, 3), Mod(1, 3)*y^2 + Mod(1, 3))

I agree it is a bit ugly.