On Jan 26, 2009, at 3:44 AM, Harald Schilly wrote: > > Hi, on the public bug tracker I got this one: > http://spreadsheets.google.com/ver? > key=pCwvGVwSMxTzT6E2xNdo5fA&t=1232807032283000&pt=1232807012283000&dif > fWidget=true&s=AJVazbXBr2D7KZ6E3qJBWICjRrHj5pKG-Q&pli=1
I didn't know there was another "public bug tracker," but that link isn't working for me... http://trac.sagemath.org/sage_trac/ticket/5107 > > quote: > """ > A simple call to the function with an irrational number returns a list > for the infinite continued fractions, with the last digit or two > incorrect. > > For exapmle: > > continued_fraction(sqrt(2)) > [1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1] > > the last two digits are incorrect > > continued_fraction(sqrt(109)) > [10, 2, 3, 1, 2, 4, 1, 6, 6, 1, 4, 2, 1, 3, 2, 20, 3] > > the last digit (3) is incorrect > """ > > Interestingly, the doctests in > http://hg.sagemath.org/sage-main/file/b0aa7ef45b3c/sage/rings/arith.py > / continued_fraction_list(...) > clearly state that this is correct. > > If i read the code correctly, the symbolic expression is evaluated > with limited precision. I think it should stated in the doctests that > it is an approximation (line #2676 -> "# if x is a > SymbolicExpression, try coercing it to a real number") - or I'm wrong > or is this a bug? Yes, this is a bug. It looks like its not correctly taking into account the uncertainty in the last digit, but it could be intermediate rounding issues as well. Interestingly enough sage: continued_fraction(QQ(RR(sqrt(2)))) [1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2] sage: continued_fraction(RR(sqrt(2)).exact_rational()) [1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 2, 7, 1, 2, 33, 2, 7, 5, 2, 1, 1, 16, 2] Of course ideally it could directly compute the continued fraction of sqrt(2), but that wouldn't fix this bug. - Robert --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
