Hi Jenny,
Since the base ring of E is QQ, what do you expect to get for an
input polynomial over Qt? A "feature" of Sage over, say, Magma,
is that the the tracebacks are long (allowing debugging).
Perhaps your entirely valid criticism is that the error in "+" is too
late: some checking that the base ring of the polynomial equals
the base ring of the curve (or that maps canonically to it) would
pick up the error at the correct point and returns a more
meaningful error message.
Another problem is that if I base extend to Qt, then isogeny is
no longer defined:
sage: Et = E.base_extend(Qt)
sage: Et.isogeny?
This seems to be a problem with the EllipticCurve constructor,
not isogeny:
sage: type(Et)
<class
'sage.schemes.elliptic_curves.ell_generic.EllipticCurve_generic'>
In particular, a line for rings.is_Field(x) needs to be added in here
to returns
an EllipticCurve_field:
if rings.is_Ring(x):
if rings.is_RationalField(x):
return ell_rational_field.EllipticCurve_rational_field(x,
y)
elif rings.is_FiniteField(x) or (rings.is_IntegerModRing(x)
and x.characteristic().is_prime()):
return ell_finite_field.EllipticCurve_finite_field(x, y)
elif rings.is_pAdicField(x):
return ell_padic_field.EllipticCurve_padic_field(x, y)
elif rings.is_NumberField(x):
return ell_number_field.EllipticCurve_number_field(x, y)
return ell_generic.EllipticCurve_generic(x, y)
Cheers,
David
On Sep 9, 10:51 am, "J. Cooley" <j.a.coo...@warwick.ac.uk> wrote:
> Hi,
>
> Here is an example:
>
> sage: Qt = Frac(PolynomialRing(QQ,'t'))
> sage: t = Qt.gen()
> sage: R = PolynomialRing(Qt,'X')
> sage: X = R.gen()
> sage: k2 = X^2 -732*X + 94752
> sage: E = EllipticCurve('11a1')
> sage: E.isogeny(kernel=k2, model = "minimal")
>
> Result: horrible, horrible error!
>
> Thanks,
> Jenny
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