There are indeed two things going on: the gp interpreter and the pari
library, You can use pari.set_real_precision() as you say.
I was mixing the two up. But in the example:
----------------------------------------------------------------------
| SAGE Version 3.1.1, Release Date: 2008-08-17 |
| Type notebook() for the GUI, and license() for information. |
----------------------------------------------------------------------
sage: pari.set_real_precision(200)
28
sage: E=EllipticCurve('37a1')
sage: P=E.gens()[0]
sage: P.height()
0.0511114082399688
Here we are using the pari library, not gp, so gp.set_real_precision()
does not help: the key line is
return self.new_gen(ellheight0(self.g, t0, flag, prec))
in the function ellheight(), but the precision parameter is *not*
being passed correctly.
John
2008/8/26 William Stein <[EMAIL PROTECTED]>:
>
> On Tue, Aug 26, 2008 at 4:23 AM, John Cremona <[EMAIL PROTECTED]> wrote:
>>
>> I already had a quick look at this when Hakan first posted, but came
>> to no instant conclusion --
>
> Given that the first output has the right precision and the second doesn't,
> it's surely a simple to fix caching issue.
>
>> except that there are quite a few
>> functions in the Sage-pari interface where precision is impossible or
>> difficult to set as one would hope.
>
> ? I think every Pari C library interface for which precision makes sense
> has precision as a parameter. I think the way the wrapper code works
> is the same as the way gp works -- you do
>
> sage: old = pari.set_real_precision(100)
> sage: pari comp
> sage: pari.set_real_precision(old)
>
>>
>> For example:
>> sage: P=EllipticCurve('37a1').gens()[0]; P.height()
>> 0.0511114082399688
>>
>> The method ellheight of sage.libs.pari.gen.gen has no prec parameter
>> though the pari function it calls does. I'm sure there are other
>> places where the same happens. We could fix them piecemeal, or fo
>> through the whole pari interface systematically, which would be a big
>> job!
>
> Or just use pari.set_real_precision. This is orthogonal though to the issue.
> In pari when you ask for a given precision it can easily just give you more.
> Sage shouldn't do that, so we have to round the output of pari in some cases.
>
> William
>
>>
>> John
>>
>> 2008/8/26 William Stein <[EMAIL PROTECTED]>:
>>>
>>> On Fri, Aug 15, 2008 at 1:57 AM, Håkan Granath
>>> <[EMAIL PROTECTED]> wrote:
>>>>
>>>> Hi,
>>>>
>>>> Is this a bug or am I doing something stupid? I get different
>>>> precisions the first and second time I run the same command.
>>>>
>>>> ----------------------------------------------------------------------
>>>> | SAGE Version 3.0.6, Release Date: 2008-07-30 |
>>>> | Type notebook() for the GUI, and license() for information. |
>>>> ----------------------------------------------------------------------
>>>>
>>>> sage: E = EllipticCurve('37a')
>>>> sage: E.period_lattice().basis(prec=30)
>>>>
>>>> (2.993458646231959629832009979452508177797583791370132985340523378563250356987,
>>>>
>>>> 2.451389381986790060854224831866525225349617289144796614656471406129152899999*I)
>>>> sage: E.period_lattice().basis(prec=30)
>>>>
>>>> (2.9934586462319596298320099794525081777975837913701329853405233785632503569866829041203940673970514734358405271049472881941443872373720252543753766710932613753043332505965246252164473069072694510749057806365610445781725817135182427934263132488980086942438020870431669315,
>>>>
>>>> 2.4513893819867900608542248318665252253496172891447966146564714061291528999992568928911321280291810887126842188696618479754751998666167558016789381647830306324546902881738259304962523119593946698932473794558796569481958707269691493740581897037588157844669302474334546641*I)
>>>>
>>>>
>>>> Best regards,
>>>>
>>>> Håkan
>>>
>>>
>>> This is definitely a bug. The output precision should be as given by
>>> the prec option. The bug is caused by a mistake in the caching code,
>>> surely. This will likely be easy to fix. This is now
>>> trac #3954:
>>>
>>> http://trac.sagemath.org/sage_trac/ticket/3954
>>>
>>> >
>>>
>>
>> >
>>
>
>
>
> --
> William Stein
> Associate Professor of Mathematics
> University of Washington
> http://wstein.org
>
> >
>
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