Re: Point multiplication on elliptic curves over Q_{p} (fwd)

[Karim BELABAS <Karim.Belabas@math.u-psud.fr>]

On Tue, 18 Jun 2002, Iftikhar Burhanuddin wrote:
>> On Fri, 14 Jun 2002, Iftikhar Burhanuddin wrote:
>>> Say f is an elliptic curve over Q_{p} and P is a point on the curve,
>>> e is the reduced elliptic curve,
>>> nump are the number of points on e [nump = p+1-ellap(f,p)],
>>> randno1 and randno2 are randomly generated integers.
>>>
>>> P1 = ellpow(f,P,nump);
>>> P2 = ellpow(f,P1,nump);
>>> P3 = ellpow(f,P,nump*nump);
>>>
>>> I would expect P2 and P3 to be equal but they are not. I can't figure out
>>> why. Also...
>>
>> Which version of GP, on which architecture ?  I cannot reproduce your problem
>> with any of pari-2.2.3, 2.1.2, or 2.1.3 on either Solaris or Linux.
>
> gp/pari calculator version 2.2.2 (alpha)
> cygwin
> windows 2000 professional
> pentium III

Now I can reproduce it. There was a nasty bug in the addition of p-adic and
rational numbers, introduced in version 2.2.2.alpha and fixed in the next
update 2.2.3.

You should upgrade to a more recent development release, for instance from
CVS, or use a binary from the stable branch (the 2.1.x series).

Cheers,

    Karim.
-- 
Karim Belabas                    Tel: (+33) (0)1 69 15 57 48
Dép. de Mathematiques, Bat. 425  Fax: (+33) (0)1 69 15 60 19
Université Paris-Sud             Email: Karim.Belabas@math.u-psud.fr
F-91405 Orsay (France)           http://www.math.u-psud.fr/~belabas/
--
PARI/GP Home Page: http://www.parigp-home.de/