Re: poldisc() problem

[Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr>]

On Tue, Jan 19, 2010 at 07:47:35AM +0100, Lorenz Minder wrote:
> Hi,
> 
> I'm having trouble with poldisc() in pari-svn. It works fine for me
> with pari-2.3.4:
> 
> ? f = x^3 + Mod(2, 3)*x^2
> %1 = x^3 + Mod(2, 3)*x^2
> ? poldisc(f)
>   ***   at top-level: poldisc(f)
>   ***                 ^----------
>   *** poldisc: impossible inverse modulo: Mod(0, 3).
>   ***   Break loop: type <Return> three times, or Control-d, to go back to GP)
> break> 

Try the following:
? f = (x^3 + x^2)*Mod(1,3)
%1 = Mod(1, 3)*x^3 + Mod(1, 3)*x^2
? poldisc(f)
%2 = 0

Using mixed-type polynomial is not well-supported because you cannot
tell whether coefficients are 0. for example if f = x^3 + Mod(2, 3)*x^2
the its derivative is
? f'
%2 = 3*x^2 + Mod(1, 3)*x
? poldegree(f')
%3 = 2
but it should be treated as a degree 1 poynomial.

Cheers,
Bill.