On Fri, May 1, 2009 at 5:13 PM, mabshoff <mabsh...@googlemail.com> wrote:
>
> While going over the open tickets in 4.0 I noticed this ticket:
>
> #5943 (Sage 3.4.2.a0: prime_pi(2^50) segfaults)
>
> If someone could take a stab at that it would be nice since that is
> brand new code and ought to be a little bit more stable than that. I
> am waiting on a fix for #5952 in the morning, i.e. Saturday, so some
> hero might want to earn some brownie points over night :)
>
Brownies are overrated.
I played around with prime_pi() for a while, both on sage.math and on
my laptop at the office (macbook running 32-bit archlinux). I didn't
manage to get a segfault on either machine with prime_pi(2^50). I
guess that's the good news? Anyway, the bad news is that the answers
returned do not agree between the two machines, e.g.
{{{
# on sage.math
sage: time prime_pi(2^50)
CPU times: user 4854.46 s, sys: 3.17 s, total: 4857.63 s
Wall time: 4857.73 s
33483379603407
#
# on my laptop
sage: time prime_pi(2^50)
CPU times: user 5555.60 s, sys: 7.81 s, total: 5563.40 s
Wall time: 5598.64 s
21969300962685
}}}
I'm pretty sure that the sage.math answer is more likely to be the
right one. You can maybe guess from the timings why I didn't try
prime_pi(2^51). I have, however, tried smaller values. I'm going to
put that data up on the trac ticket.
I have absolutely no idea what's wrong, but something definitely is,
and hopefully this will help someone fix it.
Best,
Alex
--
Alex Ghitza -- Lecturer in Mathematics -- The University of Melbourne
-- Australia -- http://www.ms.unimelb.edu.au/~aghitza/
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