Patch posted at #5919 (and already has a positive review -- thanks, malb!)
2009/4/28 John Cremona <[email protected]>: > Alex, you have found it! The variable i in that code is undefined. > Replace it by 0 so it reads > {{{ > n1 = naInit(GF2_conv_to_long(GF2X_coeff(rep,0))) > }}} > > and then it works. > > Must run to a seminar or I would make the patch... > > John > > 2009/4/28 Alex Ghitza <[email protected]>: >> >> On Tue, Apr 28, 2009 at 12:33 AM, Martin Albrecht >> <[email protected]> wrote: >>> >>> On Monday 27 April 2009, John Cremona wrote: >>>> 2^16 is the smallest for which givaro is not used. In char.2, we switch to >>>> NTL. >>> >>> Yes, it is likely in the conversion routine from NTL to Singular. >>> >> >> I managed to track this all the way to line 379 in >> libs/singular/singular.pyx, which is >> >> n1 = naInit(GF2_conv_to_long(GF2X_coeff(rep,i))) >> >> In fact, the problem is not with naInit but with what goes into it (so >> it looks like an NTL issue). To see this, add the following two lines >> before 379: >> >> temp = GF2_conv_to_long(GF2X_coeff(rep,i)) >> print "result of conversion: %s"%temp >> >> And now run the following in Sage: >> >> {{{ >> sage: F.<a> = GF(2^16) >> sage: R.<x, y> = F[] >> sage: R({(1,2):1}) >> }}} >> >> The correct response (which occurs on some computers) is: >> >> {{{ >> result of conversion: 1 >> x*y^2 >> }}} >> >> The incorrect response (caught by John and also occuring on sage.math) is: >> >> {{{ >> result of conversion: 0 >> 0*x*y^2 >> }}} >> >> Somehow NTL takes the coefficient 1 and messes it up to get 0, and >> this is machine-dependent. This is as far as my detective skills go. >> I don't even know how to check whether the problem is in GF2X_coeff or >> in GF2_conv_to_long, let alone how to fix this. Hopefully someone >> else can figure it out. >> >> Best, >> Alex >> >> >> >> -- >> Alex Ghitza -- Lecturer in Mathematics -- The University of Melbourne >> -- Australia -- http://www.ms.unimelb.edu.au/~aghitza/ >> >> >> >> > --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
