Changes between Initial Version and Version 4 of Ticket #7736


Ignore:
Timestamp:
02/11/10 15:59:07 (9 years ago)
Author:
cremona
Comment:

It may well be that the short-term fix I put in at #7097 is not yet good enough. [It is short-term since the latest version of pari have fixed some bugs which arose for non-monic polynomials, which is why the patch I put in at #7097 made sure that pari was only called to factor monic ones.]

I just had a possibly worse example, and found this ticket while looking to see if I should open a new one:

sage: E = EllipticCurve('4900a2')
sage: f = E.division_polynomial(9)
sage: K3.<z> = CyclotomicField(3)
sage: ff = f.change_ring(K3)
sage: ff.degree()
40
sage: [g.degree() for g,e in ff.factor()]
[1, 3, 9, 40]

I factor a degree 40 polynomial and the returned factors have degrees 1,3,9,40! Even if I make the polynomial monic (above it has leading coefficient 9) it is no better:

sage: x = f.parent().gen()
sage: g = 9^39 * f(x/9)
sage: all([c.is_integral() for c in g.coefficients()])
True
sage: [h.degree() for h,e in g.change_ring(K3).factor()]
[1, 3, 9, 40]

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  • Ticket #7736

    • Property Owner changed from tbd to cremona
    • Property Milestone changed from to sage-4.3.1
  • Ticket #7736 – Description

    initial v4  
    1414}}}
    1515you get a linear factor and a degree 10 factor, where both are irreducible.
     16
     17I fear it is no good asking for an upstream fix, since they (pari) have already fixed it but we are not using the fixed version. See #7097 for more details.