Thanks David. I just reported the bug to PARI.
Rob
On Sat, Feb 17, 2018 at 10:04 AM, David Loeffler <d.a.loeff...@warwick.ac.uk
> wrote:
> This is a bug in PARI, rather than in Sage, apparently:
>
> GP/PARI CALCULATOR Version 2.9.4 (released)
>
> amd64 running linux (x86-64/GMP-6.1.0 kernel) 64-bit version
>
> [...]
>
> ? nffactor(y^8 - y^6 + y^4 - y^2 + 1, x^4 + 1) \\ works
>
> %1 =
>
> [x^2 + Mod(-y^5, y^8 - y^6 + y^4 - y^2 + 1) 1]
>
>
> [ x^2 + Mod(y^5, y^8 - y^6 + y^4 - y^2 + 1) 1]
>
>
> ? nffactor(y^8 - y^6 + y^4 - y^2 + 1, x^4 - 1) \\ boom
>
> *** at top-level: nffactor(y^8-y^6+y^4
>
> *** ^--------------------
>
> *** nffactor: inconsistent concatenation t_VEC (2 elts) , t_COL (2
> elts).
>
> *** Break loop: type 'break' to go back to GP prompt
>
>
>
> On 16 February 2018 at 16:54, <robert.poll...@gmail.com> wrote:
>
>> The following code crashes (in Sage 8.1 and on CoCalc):
>>
>> sage: K=CyclotomicField(20)
>> sage: R.<x>=PolynomialRing(K)
>> sage: (x^4-1).factor()
>> ------------------------------------------------------------
>> ---------------
>> PariError Traceback (most re
>> cent call last)
>> <ipython-input-3-12edfe8f4001> in <module>()
>> ----> 1 (x**Integer(4)-Integer(1)).factor()
>>
>> /ext/sage/sage-8.1/src/sage/rings/polynomial/polynomial_element.pyx in
>> sage.rings.polynomial.polynomial_element.Polynomi
>> al.factor (build/cythonized/sage/rings/polynomi
>> al/polynomial_element.c:39428)()
>> 4127 # polynomial instead.
>> 4128 Rpari = R.pari_polynomial("y")
>> -> 4129 G = list(Rpari.nffactor(f))
>> 4130 # PARI's nffactor() ignores the unit, _f
>> actor_pari_helper()
>> 4131 # adds back the unit of the factorization.
>>
>> cypari2/auto_gen.pxi in cypari2.gen.Gen_auto.nffactor()
>>
>> cypari2/handle_error.pyx in cypari2.handle_error._pari_err_handle()
>>
>> PariError: inconsistent concatenation t_VEC (2 elts) , t_COL (2 elts)
>>
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