On 17 February 2015 at 09:06, John Cremona <john.crem...@gmail.com> wrote:
> Thanks, Anton -- I have forwarded to sage-devel and flint-devel and
> we'll try to get this fixed before the release of 6.5.
Too late, it was released overnight.
>
> John Cremona
>
> On 16 February 2015 at 23:54, Anton Mellit <mel...@gmail.com> wrote:
>> Here is the code:
>> R.<q>=QQ[]
>> X=3*q^12 - 8*q^11 - 24*q^10 - 48*q^9 - 84*q^8 - 92*q^7 - 92*q^6 - 70*q^5 -
>> 50*q^4 - 27*q^3 - 13*q^2 - 4*q - 1
>> Y=q^13 - 2*q^12 + 2*q^10 - q^9
>> print gcd(X,Y)
>> print X(1)
>> Here is the output:
>> q - 1 -510
>> The bug is extremely serious because it affects all computations with
>> rational functions. It is also quite rare, I believe. I traced it down to
>> the function _fmpz_poly_gcd_heuristic in FLINT. The bug is triggered when
>> the heuristic algorithm fails, one of the divisibility checks fails, but
>> still the value is returned as o.k.
>> The fix is easy, just one line needs to be added
>> if (divides) /* quotient really was exact */ { --->>>>> divides=0;
>>
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