On Wednesday 10 September 2008, John Cremona wrote:
> 2008/9/10 Martin Albrecht <[EMAIL PROTECTED]>:
> > On Wednesday 10 September 2008, John Cremona wrote:
> >> 2008/9/10 Nick Alexander <[EMAIL PROTECTED]>:
> >> > On 10-Sep-08, at 1:49 AM, Martin Albrecht wrote:
> >> >> On Wednesday 10 September 2008, mabshoff wrote:
> >> >>> This is double plus not good.
> >> >>>
> >> >>> {{{
> >> >>> sage: GF(109)['x', 'y'](-10)
> >> >>> -10
> >> >>> sage: GF(109)['x'](-10)
> >> >>> 99
> >> >>>
> >> >>> }}}
> >> >>
> >> >> I don't see the problem, since -10 == 99 mod GF(109).Even if it is
> >> >> undesired
> >> >> that they print differently how come it is 'major'?
> >> >
> >> > Okay, maybe it is not major. For internal reasons, I am very
> >> > unsettled to get back different representations for the same thing.
> >> > Try:
> >> >
> >> > {{{
> >> > sage: GF(109)['x', 'y'](-10)
> >> > -10
> >> > sage: GF(109)['x', 'y'](-10).constant_coefficient()
> >> > 99
> >> > }}}
> >> >
> >> > I can't see how this won't bite someone in the ass sometime.
> >>
> >> Maybe. As far as I can see the _repr_() function on the (constant)
> >> poly just gets a string from singular, so is relying on singular's
> >> representation for integers mod 109. While the constant_coefficient()
> >> function is returning a Sage object. There does not seem to be a
> >> method for turning the singular form into a Sage polynomial.
> >
> > Of course, I *could* write our own _repr_ function instead of just using
> > whatever Singular returns back.
>
> Wouldn't it be better to write a conversion from singular to a Sage
> type? Or would that be impossibly complicated (I have no idea how
> many Singular types there are, but all we need is a conversion from
> MPolynomial_libsingular to start with).
I don't understand, MPolynomial_libsingular (libsingular + wrapper) is the
Sage type, just like GMP integers + wrapper is the Sage type.
Cheers,
Martin
--
name: Martin Albrecht
_pgp: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x8EF0DC99
_www: http://www.informatik.uni-bremen.de/~malb
_jab: [EMAIL PROTECTED]
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