Although it is frustrating to have learned this only hours after a
release (which had at least 3 rc's first), please can we have a
bug-fix release as soon as Bill has patched Flint? No Sage code would
need to be changed, though adding a doctest with this example would be
a good idea.
John
On 17 February 2015 at 10:06, Bill Hart <goodwillh...@googlemail.com> wrote:
> I can confirm this is definitely a bug in flint. And the fix is absolutely
> correct. Thanks to Anton Mellit for not only figuring out which library was
> at fault, but actually tracing it to an individual line of C code!!
>
> It is a rare corner case, but very serious.
>
> I will issue a patch release with the fix as soon as possible.
>
> Bill.
>
> On Tuesday, 17 February 2015 10:06:11 UTC+1, John Cremona wrote:
>>
>> If ever there was a blocker, surely this is it!
>>
>> John
>>
>>
>> ---------- Forwarded message ----------
>> From: Anton Mellit <mel...@gmail.com>
>> Date: 16 February 2015 at 23:54
>> Subject: [sage-support] Bug in polynomial GCD (FLINT)
>> To: sage-s...@googlegroups.com
>>
>>
>> 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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