perhaps i should have posted to sage-devel instead ? i don't even know how to "properly" report a bug.
On 10 sep, 18:53, Pierre <[EMAIL PROTECTED]> wrote: > hi there, > > i thought i'd report this bug, even though it's hard to reproduce and > not well-identified. I have a ring R of type: > > Fraction Field of Multivariate Polynomial Ring in x0, x1, x2, x3, x4, > x0_iv, x1_iv, x2_iv, x3_iv, x4_iv over Cyclotomic Field of order 4 and > degree 2 > > (the _iv variables will play no role in the sequel -- not that it > matters.) > > And I have a list L of 64 matrices in MatrixSpace(R, 2). > When i try sum(L), I get: > > /home/pedro/Bureau/sage-3.0.2-ubuntu32-intel-i686-Linux/local/lib/ > python2.5/site-packages/sage/rings/fraction_field_element.py in > _add_(self, right) > 298 numer = numer // new_gcd > 299 denom = denom // new_gcd > --> 300 return FractionFieldElement(self.parent(), > numer, denom, coerce=False, reduce=False) > 301 # else: no reduction necessary > 302 except AttributeError: # missing gcd or quo_rem, > don't reduce > > /home/pedro/Bureau/sage-3.0.2-ubuntu32-intel-i686-Linux/local/lib/ > python2.5/site-packages/sage/rings/fraction_field_element.py in > __init__(self, parent, numerator, denominator, coerce, reduce) > 65 pass > 66 if self.__denominator.is_zero(): > ---> 67 raise ZeroDivisionError, "fraction field element > division by zero" > 68 > 69 def reduce(self): > > ZeroDivisionError: fraction field element division by zero > > (This is sage 3.1.1 despite the folder name.) > > If i try to do a for loop and sum the matrices one by one, i realize > that the problem is with the addition of sum(L[:49]) (call it M) and > L[49] (call it N). I can compute them separately and get the same > error message by trying M+N. > > Of course you'd like to see M and N. Well be ready for a > disappointment: M is > > [ ((37/32*I - 5/16)*x0^2*x1*x2*x3 + (-5/64*I + 7/32)*x1*x2^2*x3^2 + > (-19/32*I + 7/16)*x0^2*x1*x2*x4 + (-9/32*I - 1/16)*x0^2*x1*x3*x4 + > (-5/32*I + 13/16)*x0^2*x2*x3*x4 + (-19/8*I - 89/16)*x1^2*x2*x3*x4 + > (15/32*I - 3/8)*x1*x2^2*x3*x4 + (31/64*I - 27/64)*x2^3*x3*x4 + > (-31/32*I + 5/16)*x1*x2*x3^2*x4 + (21/32*I - 13/64)*x2*x3^3*x4 + > (-5/16*I + 15/64)*x1*x2^2*x4^2 + (-3/32*I + 1/4)*x1*x2*x3*x4^2 + > (-7/64*I + 3/64)*x1*x3^2*x4^2 + (13/64*I + 5/8)*x2*x3*x4^3)/ > (x1*x2*x3*x4) ((5/32*I - 11/32)*x0^2*x1*x2*x3 + (1/8*I - > 1/4)*x1*x2^2*x3^2 + (7/32*I + 15/32)*x0^2*x1*x2*x4 + (3/32*I - > 1/32)*x0^2*x1*x3*x4 + (9/32*I - 3/32)*x0^2*x2*x3*x4 + (-29/32*I + > 303/128)*x1^2*x2*x3*x4 + (5/16*I + 11/16)*x1*x2^2*x3*x4 + (-1/64*I + > 29/128)*x2^3*x3*x4 + (11/8*I + 1/8)*x1*x2*x3^2*x4 + (21/64*I - > 13/128)*x2*x3^3*x4 + (-17/64*I - 7/32)*x1*x2^2*x4^2 + (-7/8*I + > 7/8)*x1*x2*x3*x4^2 + (-9/64*I - 7/64)*x1*x3^2*x4^2 + (5/16*I - > 13/128)*x2*x3*x4^3)/(x1*x2*x3*x4)] > [((-5/32*I + 11/32)*x0^2*x1*x2*x3 + (-1/8*I + 1/4)*x1*x2^2*x3^2 + > (-7/32*I - 15/32)*x0^2*x1*x2*x4 + (-3/32*I + 1/32)*x0^2*x1*x3*x4 + > (-9/32*I + 3/32)*x0^2*x2*x3*x4 + (-267/32*I + 161/128)*x1^2*x2*x3*x4 + > (-5/16*I + 23/16)*x1*x2^2*x3*x4 + (1/64*I - 29/128)*x2^3*x3*x4 + > (-1/8*I + 3/2)*x1*x2*x3^2*x4 + (-21/64*I + 13/128)*x2*x3^3*x4 + > (17/64*I + 7/32)*x1*x2^2*x4^2 + (7/8*I + 7/4)*x1*x2*x3*x4^2 + (9/64*I > + 7/64)*x1*x3^2*x4^2 + (-5/16*I + 13/128)*x2*x3*x4^3)/(x1*x2*x3*x4) > ((47/32*I - 7/8)*x0^2*x1*x2*x3 + (5/64*I + 15/32)*x1*x2^2*x3^2 + > (47/32*I + 3/4)*x0^2*x1*x2*x4 + (-15/32*I + 1/2)*x0^2*x1*x3*x4 + > (-27/32*I + 1/2)*x0^2*x2*x3*x4 + (41/8*I + 49/16)*x1^2*x2*x3*x4 + > (-13/32*I + 1/16)*x1*x2^2*x3*x4 + (-27/64*I - 31/64)*x2^3*x3*x4 + > (33/32*I + 13/8)*x1*x2*x3^2*x4 + (21/32*I - 13/64)*x2*x3^3*x4 + (1/8*I > - 29/64)*x1*x2^2*x4^2 + (-83/32*I - 15/16)*x1*x2*x3*x4^2 + (-1/64*I - > 25/64)*x1*x3^2*x4^2 + (-13/64*I - 5/8)*x2*x3*x4^3)/(x1*x2*x3*x4)] > > while N is > > [ > > > > > 0 > ((-5/32*I + 11/32)*x0^2*x1*x2*x3 + (-1/8*I + 1/4)*x1*x2^2*x3^2 + > (-7/32*I - 15/32)*x0^2*x1*x2*x4 + (-3/32*I + 1/32)*x0^2*x1*x3*x4 + > (-9/32*I + 3/32)*x0^2*x2*x3*x4 + (23/32*I + 129/128)*x1^2*x2*x3*x4 + > (1/2*I - 3/16)*x1*x2^2*x3*x4 + (1/64*I - 29/128)*x2^3*x3*x4 + (-3/16*I > + 3/8)*x1*x2*x3^2*x4 + (-21/64*I + 13/128)*x2*x3^3*x4 + (17/64*I + > 7/32)*x1*x2^2*x4^2 + (1/16*I + 1/4)*x1*x2*x3*x4^2 + (9/64*I + > 7/64)*x1*x3^2*x4^2 + (-5/16*I + 13/128)*x2*x3*x4^3)/(x1*x2*x3*x4)] > [ ((5/32*I - 11/32)*x0^2*x1*x2*x3 + (1/8*I - 1/4)*x1*x2^2*x3^2 + > (7/32*I + 15/32)*x0^2*x1*x2*x4 + (3/32*I - 1/32)*x0^2*x1*x3*x4 + > (9/32*I - 3/32)*x0^2*x2*x3*x4 + (-23/32*I - 129/128)*x1^2*x2*x3*x4 + > (-1/2*I + 3/16)*x1*x2^2*x3*x4 + (-1/64*I + 29/128)*x2^3*x3*x4 + > (3/16*I - 3/8)*x1*x2*x3^2*x4 + (21/64*I - 13/128)*x2*x3^3*x4 + > (-17/64*I - 7/32)*x1*x2^2*x4^2 + (-1/16*I - 1/4)*x1*x2*x3*x4^2 + > (-9/64*I - 7/64)*x1*x3^2*x4^2 + (5/16*I - 13/128)*x2*x3*x4^3)/ > (x1*x2*x3*x4) > > 0] > > (I can provide the dumpstrings if anyone is interested in trying) > (oh and here I is sqrt(-1)) > > HOWEVER, it is in fact possible to do sum(L[30:]) + sum(L[:30]) !! > don't know whether the answer is meaningful though. In fact, other > experiments with these matrices lead me to believe that sometimes > sum() just gets the wrong answer (things that were supposed to commute > didn't commute; but they were sums of things which did commute). > > Thoughts anyone ? > > Pierre --~--~---------~--~----~------------~-------~--~----~ 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-support URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
