Re: bug in ellap

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

[John Cremona:]
> e=ellinit([1, -1, 0, -79, 289]);
> (17:00) gp > ellap(e,2)
> %39 = 1
> (17:00) gp > ellap(e,2,0)
> %40 = 1
> (17:00) gp > ellap(e,2,1)
> %41 = -1
> (17:00) gp > ellak(e,2)  
> %42 = -1
> 
> The default option on ellap gives the wrong answer here (-1 is the
> right answer!).

I introduced this one (only happens for p = 2 | Delta) when correcting
another bug : ellap yielded a SEGV when c6 was not an integer. The trivial
fix at the time was to multiply c6 by Mod(1,p) then recover an integer. Of
course when p = 2, it should have been Mod(1,8) ...

This is now corrected in the CVS archive.

> Secondly, the manual entry for ellap should stress that it gives wrong
> answers for non-minimal models (as the entry for ellak does, repeated
> in ellan).

Done.

  Karim.
__
Karim Belabas                    email: Karim.Belabas@math.u-psud.fr
Dep. de Mathematiques, Bat. 425
Universite Paris-Sud             Tel: (00 33) 1 69 15 57 48
F-91405 Orsay (France)           Fax: (00 33) 1 69 15 60 19
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