#4000: [with patch, needs work] Implement QQ['x'] via Flint ZZ['x'] +
denominator
------------------------------+---------------------------------------------
Reporter: malb | Owner: somebody
Type: enhancement | Status: new
Priority: major | Milestone: sage-wishlist
Component: basic arithmetic | Keywords:
Reviewer: | Author: Martin Albrecht
Merged: |
------------------------------+---------------------------------------------
Comment(by spancratz):
Hi Martin,
I am sorry for that. Last night and this morning I fixed another couple
of bugs. In a few minutes, I'll upload a new patch (or rather, again the
difference from the 20090911 patch). By the way, for debugging purposes
all methods in the linkage file now begin with printing the method's name
(although in all but the floordiv method, that line begins with '#').
Random (performance!, not correctness...) tests ran fine last night for
polynomials of degree 2000 for the methods ==, <, +, -, neg, *, ^. I
thought the three division methods should work fine now, until I stumbled
across the following segfault:
{{{
sage: S.<y> = QQ[]
sage: f = -3 * y^10 - 4 * y^9
sage: g = (1/2) * y^6 + 3 * y^5 + 160930 * y^4
sage: f // g
celement_floordiv
Perform pseudo division -3*x^10-4*x^9 x^6+6*x^5+321860*x^4
------------------------------------------------------------
Unhandled SIGSEGV: A segmentation fault occured in SAGE.
This probably occured because a *compiled* component
of SAGE has a bug in it (typically accessing invalid memory)
or is not properly wrapped with _sig_on, _sig_off.
You might want to run SAGE under gdb with 'sage -gdb' to debug this.
SAGE will now terminate (sorry).
------------------------------------------------------------
}}}
This strikes me as very odd because the segfault seems to occur in the
call ``fmpz_poly_pseudo_div(q.num, &m, a.num, b.num)`` with ``a.num`` the
polynomial ``-3*x^10-4*x^9`` and ``b.den`` the polynomial
``x^6+6*x^5+321860*x^4``. Perhaps you could have a look at this one?
I haven't looked at the two gcd methods yet, but I'll do that later today
or tomorrow.
As the last question about the implementation (for this method), I noticed
that polynomials over QQ in SAGE have the method ``denominator``, which
clearly this implementation should overwrite. On which level/ in which
file should this be done?
Finally, here are the performance timings, in each case for ten random
polynomials of degree 2000, first the time for the generic implementation
and then the time for this implementation with FLINT:
- ``==`` - 20µs, 1µs
- ``<`` - 20µs, 1µs
- ``+`` - 400µs, 100µs
- ``-`` - 400µs, 100µs
- ``neg`` - 20ms, 20µs
- ``*`` - 500ms, 1ms
- ``^`` (to the 4th power) - 15s, 30µs
Kind regards,
Sebastian
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/4000#comment:16>
Sage <http://sagemath.org/>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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