I consider this as a bug, too. My guess is, that it comes from the Singular
interface:
sage: R.<x,y> = PolynomialRing(QQ, order='negdeglex')
sage: f = 1 + x
sage: I = R.ideal(x^2)
sage: import sage.libs.singular.function_factory
sage: reduce = sage.libs.singular.function_factory.ff.reduce
sage: reduce(f, I)
1
but:
SINGULAR / Development
A Computer Algebra System for Polynomial Computations / version 4.1
.1
0<
by: W. Decker, G.-M. Greuel, G. Pfister, H. Schoenemann \ Feb 2018
FB Mathematik der Universitaet, D-67653 Kaiserslautern \
> ring r = 0,(x, y),lp;
> poly f,g = 1+x, x^2;
> ideal I = (g);
> reduce(f,I);
x+1
Note, that in Sage f.reduce(I) returns 1, as well, even though is not
implemented as above, but using the Singular kernel function kNF. Anyway,
this seems to be a task for Singular experts.
On Monday, April 6, 2020 at 9:46:26 AM UTC+2, Yang Zhou wrote:
>
> Hi,
>
> I am trying to truncate a multi-variable polynomial by moding out higher
> order term and found
> the following (simplified) example. I am wondering if it is a bug.
>
>
> *Reproducible Example: *
>
>> R.<x,y> = PolynomialRing(QQ, order='negdeglex')
>>
> f = 1 + x
>> I = R.ideal(x^2)
>> f.mod(I)
>>
> *Expected output:*
>
>> 1 + x
>>
> *Actual output:*
>
>> 1
>>
>
>
> *Note: *
> The actual output will be 1+x when I omit the "order='negdeglex" parameter.
>
> *SageMath version:*
> SageMath version 9.0, Release Date: 2020-01-01
>
> *Operating system:*
> OS: Ubuntu 19.10 x86_64
> Kernel: 5.3.0-45-generic
>
> Best regards,
> Yang
>
--
You received this message because you are subscribed to the Google Groups
"sage-devel" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sage-devel+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/sage-devel/f1c2216c-23d9-438c-a587-7f4b92848974%40googlegroups.com.
