#13054: Pernicious bug for algebraic numbers
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Reporter: rbeezer | Owner: davidloeffler
Type: defect | Status: new
Priority: major | Milestone: sage-5.7
Component: number fields | Resolution:
Keywords: sd40.5 | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
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Comment (by nbruin):
Found in [https://groups.google.com/group/sage-
devel/browse_thread/thread/4b5aaadddf01db5d?hl=en this sage-devel thread]
{{{
sage: R.<x,y>=QQbar[]
sage: f=x^2+x^3-y^2+y^4*x^4
sage: RX=PolynomialRing(QQbar,'x')
sage: RY=PolynomialRing(QQbar,'y')
sage: x0=3+2^-8
sage: y0=RY(f((x0,y))).roots(multiplicities=False)[0]
sage: f(x+x0,y0)
}}}
sounds like it might be triggerering the same problem as reported in the
ticket.
The slightest bit of `%debug` fun shows that the problem arises here
`> /usr/local/sage/5.6rc0/local/lib/python2.7/site-
packages/sage/rings/qqbar.py(1563)do_polred()`:
{{{
1562 parent = poly.parent()
-> 1563 rev = parent(best_elt.Mod(pari_poly).modreverse().lift())
1564 return parent(best_elt), rev, parent(best)
}}}
with these inputs:
{{{
R.<y>=QQ['y']
best_elt = (1/16*y^2 - 134217728)._pari_()
pari_poly = y^4 - 4294967296*y^2 + 54265257667816538374400
rev = parent(best_elt.Mod(pari_poly).modreverse().lift())
}}}
confirming a degree mismatch problem.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13054#comment:2>
Sage <http://www.sagemath.org>
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