On 5 February 2010 16:18, William Stein <wst...@gmail.com> wrote:
> On Fri, Feb 5, 2010 at 8:12 AM, John Cremona <john.crem...@gmail.com> wrote:
>> Here's the explanation. I had thought that check=False just stops the
>> check that the equations are satisfied (I posted an examples where
>> there were no equations which perhaps hid my point; I found this
>> while constructing points on a curve in P^2). But in fact it checks
>> nothing at all.
>>
>> All I would want to do is change the line self._coords = v to
>> self._coords = list(v) at the appropriate place. If that failed, then
>> it's the user's false. In this case it did not fail and almost
>> everything worked, except that I got inconsistencies in sorting points
>> since the sort function tearted a point with _coords as list
>> differently from points with _coords as tuple!
>
> But the reason for check=False is that it is useful for writing
> internal code, where you want
> to avoid the potentially substantial overhead of operations such as "list(v)".
I did not know that was potentially expensive. If so, let the code be
as it is -- but then whenever a function has a "check-False" option
the exact correct input should be documented. Which it is NOT at
present:
sage: F = GF(2^6,'a')
sage: P2.<X,Y,Z> = ProjectiveSpace(F,2)
sage: C = Curve(X^5+11*X*Y*Z^3 + X^2*Y^3 - 13*Y^2*Z^3)
sage: C.point?
Type: instancemethod
Base Class: <type 'instancemethod'>
String Form: <bound method ProjectiveCurve_finite_field.point of
Projective Curve over Finite Field in a of size 2^6 defined by X^5 +
X^2*Y^3 + X*Y*Z^3 + Y^2*Z^3>
Namespace: Interactive
File:
/home/jec/sage-4.3.2.rc0/local/lib/python2.6/site-packages/sage/schemes/generic/scheme.py
Definition: C.point(self, v, check=True)
Docstring:
x.__init__(...) initializes x; see x.__class__.__doc__ for signature
I made assumptions about using check=False, and was wrong, and got stung!
John
>
> Maybe we need another option? E.g., check_ring or something?
>
> -- William
>
> --
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