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PARI polred() bug #13054
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comment:1
This is not the same bug as above, but could be another symptom. Still hunting for an example to grab onto. Run
which should hangup and when killed with Ctrl-C yields
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comment:2
Found in this sage-devel thread
sounds like it might be triggerering the same problem as reported in the ticket. The slightest bit of
with these inputs:
confirming a degree mismatch problem. EDIT: actually, from this example you don't see any degree mismatch problem immediately. The problem is that the minimal polynomial of |
Workaround (it's really a bug in pari) |
comment:3
Attachment: trac_13054-workaround.patch.gz Why is this a bug in PARI? It seems to me that PARI behaves as documented. The degree of the minimal polynomial is less than the degree of the field. What would you expect PARI to do in this case?
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comment:4
GP instructions illustrating the problem:
The documentation of polred promises that |
comment:5
OK sorry, I misunderstood that there was a problem with |
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Upstream: Reported upstream. No feedback yet. |
comment:8
Nils and Jeroen, THANKS for making some progress on this one. David Roe and I had some "debug fun" with this last summer and I wasn't quite able to keep up and top of what was happening, so I'm glad we've got some better ideas about the source of the problem. Hopefully this will make some matrix arithmetic over QQbar work better. Rob |
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comment:9
The workaround looks good to me. You should add a comment though saying why we do this, refering to this ticket. And of course add the obligatory doctest. |
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Author: Jeroen Demeyer |
Attachment: pari-2.5.3.p3.diff.gz Diff for the PARI spkg, for review only |
Changed upstream from Reported upstream. No feedback yet. to Fixed upstream, but not in a stable release. |
comment:12
The spkg is ready for review, but this also needs a Sage library patch. |
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comment:15
Any reviewers?... |
comment:16
Doesn't the input to |
Attachment: 13054_polredbest.patch.gz |
Reviewer: David Roe |
Merged: sage-5.8.beta2 |
PARI's
polred()
returns reducible polynomials. GP session:Upstream: http://pari.math.u-bordeaux.fr/cgi-bin/bugreport.cgi?bug=1395
This bug causes problem with arithmetic over
QQbar
:Line 1563 (5.1.beta0) of sage/rings/qqbar.py:
Here, we are calling
modreverse()
on a element of a subfield. It would make a lot of exact linear algebra much more reliable if this was resolved.Apply: attachment: 13054_polredbest.patch
spkg: http://boxen.math.washington.edu/home/jdemeyer/spkg/pari-2.5.3.p3.spkg
Upstream: Fixed upstream, but not in a stable release.
CC: @roed314
Component: number fields
Keywords: sd40.5
Author: Jeroen Demeyer
Reviewer: David Roe
Merged: sage-5.8.beta2
Issue created by migration from https://trac.sagemath.org/ticket/13054
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