[Vedran Furač] > I think that this results must be the same: > > In [3]: math.atan2(-0.0,-1) > Out[3]: -3.1415926535897931
Whether -0.0 and 0.0 are different floats internally depends on your hardware floating-point; on most machines today, they are different floats, but _compare_ equal to each other. > In [4]: math.atan2(-0,-1) > Out[4]: 3.1415926535897931 "0" and "1" are integer literals, and there is no current hardware on which -0 produces a different bit pattern internally than 0. Of course you can _want_ them to be different, but you'll hope in vain ;-) > In [5]: -0 == -0.0 > Out[5]: True You'll also find that -0.0 == +0.0 returns True, despite that atan2 may treat them differently. The IEEE 754 standard for floating-point arithmetic requires that they compare equal, BTW. > This is python 2.4.4c0 on Debian GNU/Linux. Doesn't much matter. The hardware may matter, though, and so may the C library implementing atan2, and so may the set of option flags passed to the platform C compiler when Python is compiled. For example, DEC Alpha hardware has little native support for signed zeroes, and compilers for that box accept the HW limitations by default. Bottom line: if you want atan2 to treat signed zeroes differently, never use integer arguments (or results computed from integers), and even then don't expect it to be portable. -- http://mail.python.org/mailman/listinfo/python-list
