On May 29, 10:54 pm, David Harvey <dmhar...@cims.nyu.edu> wrote: > Hmmm let me try again. Would appreciate help from people familiar with > FLINT wrapper and/or coercion system. > > sage: R.<x> = PolynomialRing(Integers(121)) > sage: S.<y> = PolynomialRing(Integers(11)) > sage: S(50*x) > 6*y > sage: R(S(50*x)) > 50*x # !!!!!! > > I think what's actually happening is that the underlying FLINT > zmod_poly object is not getting coefficients reduced into [0, 10]. > This causes other problems indirectly (e.g. #5817). I can't quite > trace why this is happening. Any ideas?
There is a also a performance issue. The following is in sage 3.4.2: sage: R.<x> = PolynomialRing(Integers(11^6)) sage: S.<y> = PolynomialRing(Integers(11^3)) sage: f = R([ZZ.random_element(11^6) for _ in range(1000000)]) sage: time g = f * f CPU times: user 0.96 s, sys: 0.01 s, total: 0.97 s Wall time: 0.96 s sage: f = S(f) sage: time g = f * f CPU times: user 0.93 s, sys: 0.00 s, total: 0.93 s Wall time: 0.93 s sage: f = S([ZZ.random_element(11^3) for _ in range(1000000)]) sage: time g = f * f CPU times: user 0.55 s, sys: 0.00 s, total: 0.55 s Wall time: 0.55 s What appears to be happening is that FLINT is using kronecker substitution for the multiplication (packing polynomials into an integer and then multiplying the integers), but in the second multiplication above it is *not* reducing mod 11^3 before doing this. Even better evidence is the following: if I install flint 1.2.5 (as per trac #5817) I get: sage: R.<x> = PolynomialRing(Integers(11^6)) sage: S.<y> = PolynomialRing(Integers(11^3)) sage: f = R([ZZ.random_element(11^6) for _ in range(1000000)]) sage: f = S(f) sage: time g = f * f sage.bin: zn_poly/src/zn_poly.h:185: zn_mod_add_slim: Assertion `x < mod->m && y < mod->m' failed. /home/dmharvey/5817/sage-3.4.2-new/local/bin/sage-sage: line 198: 16421 Aborted (core dumped) sage-ipython "$@" -i This means two things: (1) zn_poly is getting compiled with debug assertions, which it shouldn't, since this is a major performance loss, and (2) some zn_poly routine is getting called on a polynomial with non-normalised coefficients. But I still don't know exactly where the non-normalisation is happening. david --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to sage-devel-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
