[Python-Dev] Can 3.1 still be built without complex? (original) (raw)
Mark Dickinson dickinsm at gmail.com
Thu Oct 15 21:42:50 CEST 2009
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On Thu, Oct 15, 2009 at 8:17 PM, Antoine Pitrou <solipsis at pitrou.net> wrote:
(-1)**.5 (6.123031769111886e-17+1j) Don't we have a precision problem here? 0.5 is supposed to be represented exactly, isn't it?
0.5 is represented exactly, but complex.pow makes no pretence of being correctly rounded (and making it correctly rounded would likely be prohibitively expensive in terms of code size and complexity). It's using something like x*y = exp(ylog(x)) behind the scenes, at least for computing the argument of the result.
For square roots, cmath.sqrt produces better results.
Mark
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