I think everybody understands what's going on regarding ECM now,
thanks to Dima's quick answer.
Paul Zimmerman who wrote this code (and reads sage-support via a daily
digest), sent me this
note to pass on as well:
" Hi William,
please can you forward my answer below?
Thanks,
Paul
##############################################################################
The default B1 value of ecm.factor() is too large. Using B1=2 works:
sage: ecm.factor(71281426948143699070565,B1=2)
[5, 53, 337, 1873, 2833, 7507, 20037791]"
On Sun, Jan 29, 2023 at 11:54 AM G. M.-S. <lists....@gmail.com> wrote:
>
>
> Thanks Dima, you taught me something new today.
>
> Guillermo
>
> On Sun, 29 Jan 2023 at 20:50, Dima Pasechnik <dimp...@gmail.com> wrote:
>>
>> On Sun, Jan 29, 2023 at 3:04 PM G. M.-S. <lists....@gmail.com> wrote:
>> >
>> > For me, with SageMath version 9.8.beta7
>> > sage: ecm.factor(71281426948143699070565)
>> > does not return quickly either.
>> > Indeed, running
>> > sage: ecm.interact()
>> > seems to show a strange behaviour for 71281426948143699070565 when
>> > factoring the factors found.
>> > As this is probabilistic and the output changes every time, I do not copy
>> > it here.
>>
>> Basically, the default B1 value is too large in this case.
>>
>> sage: ecm.factor(71281426948143699070565,B1=200) # almost instant
>> [5, 53, 337, 1873, 2833, 7507, 20037791]
>> sage: ecm.factor(71281426948143699070565,B1=2000) # takes looong time
>>
>> the docs say:
>>
>> * "B1" -- initial lower bound, defaults to 2000 (15 digit factors).
>> Used if "factor_digits" is not specified.
>>
>> > Guillermo
>> >
>> > On Sun, 29 Jan 2023 at 15:41, Bill Witzke <bwitzk...@gmail.com> wrote:
>> >>
>> >> Hi,
>> >>
>> >> I have a hard time factoring the number 71281426948143699070565 using
>> >> ecm.factor(). No result is given after a few minutes runtime. Though,
>> >> plain factor() happily factors the number. Factoring smaller or larger
>> >> numbers work fine with ecm.factor(), too. Just the single given number
>> >> seems to be problematic.
>> >>
>> >> Am I doing something wrong? Can someone confirm?
>> >>
>> >> system:
>> >> Ubuntu 22.04
>> >> sagemath 9.5-4 (via apt)
>> >> Intel Pentium N5000
>> >> (SageMath and Python beginner)
>> >>
>> >> example code factoring numbers in the range [71281426948143699070565 -
>> >> L, 71281426948143699070565 + L]:
>> >>
>> >> # Odd number.
>> >> n = 71281426948143699070565
>> >> # Limit.
>> >> L = 2
>> >> # Iterate over interval [-L, L].
>> >> for i in range(-L, L + 1):
>> >> m = n + i
>> >> print("%d => %s" % (m, ecm.factor(m)))
>
>
>
> --
> You received this message because you are subscribed to the Google Groups
> "sage-support" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to sage-support+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/sage-support/CANnG18_HSRJZKhmC8%3DQ476x-FY9s%2BQZToXOKtk0NV1QBquUxtA%40mail.gmail.com.
--
William (http://wstein.org)
--
You received this message because you are subscribed to the Google Groups
"sage-support" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sage-support+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/sage-support/CACLE5GA34GN7_7pV2ePS33warYT6By7rMiFR7iRB9dr2zhyHZA%40mail.gmail.com.
