#11836: gens_reduced() does not handle "large" ideals
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Reporter: mirela | Owner: jdemeyer
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.7.3
Component: number fields | Keywords:
Work_issues: | Upstream: N/A
Reviewer: Marco Streng | Author: Jeroen Demeyer
Merged: | Dependencies: #11130
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Comment(by mstreng):
Replying to [comment:19 jdemeyer]
Hi Jeroen,
Thanks for the explanation. I understood all of that, except for
{{{__ideal_class_log}}} always being output and always being correct. If
it is, then what is the difference between flag=0 and flag=2? Are you
saying that there is no difference? The documentation of bnfisprincipal
from pari 2.5.0 seems to confirm what you are saying. I just realised that
I was reading the documentation from 2.3.5, which suggested otherwise.
I guess that leaves only my other reason for removing flag=1:
The warning disappears if you replace flag=1 by 0, 2 or 3. This is because
you only get the warning when you ask for a generator, but don't get it
and don't demand it (i.e., if you choose flag=1 and the ideal is too big).
The warning is confusing and worried me as a user. So I would like to
either have it extensively documented in this patch, or removed. And it
can be removed simply by never using flag=1, but always 0, 2, or 3.
If you simply replace flag=1 by 0, 2 or 3, then that slows your patch down
in some cases. However, you could do flag=3 if gens_needed=True, and
flag=0 otherwise. In other words, call bnfisprincipal only 1 time during
{{{__cache_...}}} with the flag directly depending on gens_needed. That
would not slow things down. In fact, it would speed things up in case of
gens_needed=True and a big ideal.
Marco
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11836#comment:21>
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