On Mar 11, 10:49 pm, "Paddy" <[EMAIL PROTECTED]> wrote: > On Mar 11, 9:28 pm, Paul Rubin <http://[EMAIL PROTECTED]> wrote: > > > Dennis Lee Bieber <[EMAIL PROTECTED]> writes: > > > > Pardon? What is "the right thing with signed zeros"... In the last > > > 30 years I've been on machines that normalize floating zero into a true > > > zero (all bits are zero: mantissa, exponent, and sign). This is the > > > first time I've even seen a variable output as a negative 0.0! > > > Most machines these days use IEEE 754 which supports negative zero. > > >http://en.wikipedia.org/wiki/Negative_zero > > Isn't negative zero mathematically the same as zero? Isn't -0 just an > artefact of the representation of floating point numbers? Shouldn't > f(0) == f(-0) for all functions f? > I read the wikipedia article about meteorologists using -0 to denote a > negative number rounded to zero for the purposes of binning, i.e. if > you want to tally days with temperature above and below zero, but it > doesn't seem right. You should arrange for any temperature to be in > only one range and record temperatures to their determined accuracy. a > temperature of zero would only be in one bin and if a temperature is > read as -0.2 and th rounding says it should be taken as zero then it > should go in the same bin as any positive reading that is rounded to > zero. > Getting back to Python, shouldn't we strive to remove any distinction? > a zero is a zero regardless of sign and a function like atan returning > one of two different vaues for an argument of zero is actually > mathematically not a bad thing to do? > > - Paddy.
A big thanks to Paul and Andre, I think I have it now. The OP is investigating multivalued functions where the function converges to different values when approached from different directions. Floating point arithmetic being a best compromise solution to the rational number system, distinguishes between zero and minus zero as an important part of the compromise. The OP wants to compute a function of zero and minus zero distinctly and is hampered by Python not preserving the zero/minus zero distinction in some cases - hence it being a bug. Swell, Ta! - Paddy. Hey, I'm still learnin'. Sweet! -- http://mail.python.org/mailman/listinfo/python-list
