On Apr 13, 2008, at 9:46 PM, William Stein wrote: > > On Sun, Apr 13, 2008 at 9:37 PM, <[EMAIL PROTECTED]> wrote: >> >> sage: Q.<x,y> = QQ['x,y'] >> sage: R.<X,Y> = Q.quo(Q.ideal(x^2 + y^2 -1)) >> sage: X/2 >> >> --------------------------------------------------------------------- >> ------ >> <type 'exceptions.NotImplementedError'> Traceback (most recent >> call last) >> >> /home/boothby/.sage/<ipython console> in <module>() >> >> /home/boothby/.sage/element.pyx in >> sage.structure.element.RingElement.__div__ (sage/structure/ >> element.c:9080)() >> >> /home/boothby/.sage/coerce.pyx in >> sage.structure.coerce.CoercionModel_cache_maps.bin_op_c (sage/ >> structure/coerce.c:5055)() >> >> /home/boothby/.sage/element.pyx in >> sage.structure.element.RingElement.__div__ (sage/structure/ >> element.c:9063)() >> >> /home/boothby/.sage/coerce.pxi in sage.structure.element._div_c >> (sage/structure/element.c:16174)() >> >> /home/boothby/sage/local/lib/python2.5/site-packages/sage/rings/ >> quotient_ring_element.py in _div_(self, right) >> 114 if not right.is_unit(): >> 115 raise ZeroDivisionError >> --> 116 raise NotImplementedError >> 117 >> 118 def __int__(self): >> >> <type 'exceptions.NotImplementedError'>: >> >> >> I'd understand if I were trying to divide by a non-unit, or even >> a unit polynomial. But I'm trying to divide by a unit in the base >> ring -- shouldn't that work? Is this a problem in the coercion >> model, or is it validly not implemented? >> > > It's simply not implemented. Implement it and post a patch.... :-)
I would add that it needs to be implemented carefully--it will be easy to create infinite loops as division creates fraction-field elements, so you can't just invert and cast. > The source code for the function _div_ that is called is > > sage: X._div_?? > Source: > def _div_(self, right): > if not right.is_unit(): > raise ZeroDivisionError > raise NotImplementedError > > which does *not* presently try to invert right if it does happen to > be a unit > in the base ring. Why? Because it's not implemented yet. > Your best bet is to either implement better functionality > for computing in quotient rings or to type > > sage: X * (1/2) > 1/2*X > > By the way, looking at the file quotient_ring_element.py, I would > bring the doctest coverage to 100% before adding or subtracting > any code from that file. Right now coverage is a terrible 24%. > > -- william > > --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com 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 -~----------~----~----~----~------~----~------~--~---
