Bill Allombert on pari-dev pointed out that Sage's current behaviour
of, when construction an elliptic curve over Q from a j-invariant,
automatically finding the minimal quadratic twist, has the side-effect
of factoring j and j-1728, which adds to the complexity of what would
otherwise be a trivial operation. (See lines 423-455 of
sage/schemes/elliptic_curves/constructor.py.) So perhaps we should
either not do this at all, or have it as an option. It would be easy
to do that in the function that does the work, EllipticCurve_from_j(),
but less natural with normal route via EllipticCurve(j=...) which
would also need a new parameter to be passed to the other function.
On Sat, Jun 9, 2012 at 6:31 AM, John Cremona <john.crem...@gmail.com> wrote:
> Bill Allombert on pari-dev pointed out that Sage's current behaviour
> of, when construction an elliptic curve over Q from a j-invariant,
> automatically finding the minimal quadratic twist, has the side-effect
> of factoring j and j-1728, which adds to the complexity of what would
> otherwise be a trivial operation. (See lines 423-455 of
> sage/schemes/elliptic_curves/constructor.py.) So perhaps we should
> either not do this at all, or have it as an option. It would be easy
> to do that in the function that does the work, EllipticCurve_from_j(),
> but less natural with normal route via EllipticCurve(j=...) which
> would also need a new parameter to be passed to the other function.
> Any thoughts?
> John
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On Sat, Jun 9, 2012 at 5:02 PM, David Roe <roed.m...@gmail.com> wrote:
> We could have a "minimal_twist" option to the EllipticCurve constructor,
> which would be false by default.
> David
I think it should be *true* by default, for backwards compatibility,
and because usually this is what you want (nobody has complained).
We should definitely have both a fast and less clean version (like
PARI no doubt will default to), and a nicer but slower version (that
pari will probably never have), and the nice version should I think be
the default.
> On Sat, Jun 9, 2012 at 6:31 AM, John Cremona <john.crem...@gmail.com> wrote:
>> Bill Allombert on pari-dev pointed out that Sage's current behaviour
>> of, when construction an elliptic curve over Q from a j-invariant,
>> automatically finding the minimal quadratic twist, has the side-effect
>> of factoring j and j-1728, which adds to the complexity of what would
>> otherwise be a trivial operation. (See lines 423-455 of
>> sage/schemes/elliptic_curves/constructor.py.) So perhaps we should
>> either not do this at all, or have it as an option. It would be easy
>> to do that in the function that does the work, EllipticCurve_from_j(),
>> but less natural with normal route via EllipticCurve(j=...) which
>> would also need a new parameter to be passed to the other function.
>> Any thoughts?
>> John
>> --
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-- William Stein
Professor of Mathematics
University of Washington
http://wstein.org
Thanks -- I have created ticket #13100 for this and will deal with it,
as well as #11773 while I am at it (but with separate patches). Just
don't mention #128.
John
On 10 June 2012 15:56, William Stein <wst...@gmail.com> wrote:
> On Sat, Jun 9, 2012 at 5:02 PM, David Roe <roed.m...@gmail.com> wrote:
>> We could have a "minimal_twist" option to the EllipticCurve constructor,
>> which would be false by default.
>> David
> I think it should be *true* by default, for backwards compatibility,
> and because usually this is what you want (nobody has complained).
> We should definitely have both a fast and less clean version (like
> PARI no doubt will default to), and a nicer but slower version (that
> pari will probably never have), and the nice version should I think be
> the default.
>> On Sat, Jun 9, 2012 at 6:31 AM, John Cremona <john.crem...@gmail.com> wrote:
>>> Bill Allombert on pari-dev pointed out that Sage's current behaviour
>>> of, when construction an elliptic curve over Q from a j-invariant,
>>> automatically finding the minimal quadratic twist, has the side-effect
>>> of factoring j and j-1728, which adds to the complexity of what would
>>> otherwise be a trivial operation. (See lines 423-455 of
>>> sage/schemes/elliptic_curves/constructor.py.) So perhaps we should
>>> either not do this at all, or have it as an option. It would be easy
>>> to do that in the function that does the work, EllipticCurve_from_j(),
>>> but less natural with normal route via EllipticCurve(j=...) which
>>> would also need a new parameter to be passed to the other function.
>>> Any thoughts?
>>> John
>>> --
>>> You received this message because you are subscribed to the Google Groups
>>> "sage-nt" group.
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>> --
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> --
> William Stein
> Professor of Mathematics
> University of Washington
> http://wstein.org
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