On Wed, 18 Jan 2006, Steven D'Aprano wrote: > On Tue, 17 Jan 2006 23:34:40 +0000, Tom Anderson wrote: > >>>> So I don't really know what point you are making. What solution(s) for >>>> 1**0.5 were you expecting? >>> >>> He's probably getting at the fact that if you're dealing with complex >>> numbers, square root get a lot more complicated: >>> >>> http://mathworld.wolfram.com/SquareRoot.html >>> >>> But still, that doesn't change the fact that x**0.5 as is meant here is >>> the principal (positive) real square root, and that can be true whether >>> your hierarchy of numeric types includes a complex type or not. >> >> Er, actually, i meant to write -1, but evidently missed a key, and failed >> to check what i'd written. > > Since exponentiation has higher priority than negation, -1**0.5 is -1.0 in > both Python and ordinary mathematics. > > Perhaps you meant to write (-1)**0.5,
Yes. [FX: bangs head on keyboard] I'm still getting this wrong after all these years. > in which case Python developers have a decision to make: should it > assume real-valued maths unless explicitly told differently, and hence > raise an exception, or coerce the result to complex? Precisely. > In this case, Python raises an exception, as it should, unless you > explicitly uses complex numbers. That's the best behaviour for the > majority of people: most people don't even know what complex numbers > are, let alone want to deal with them in their code. Python, after all, > is not Mathematica. I think i agree with you, as a matter of practical value. However, this does go against the whole numeric unification thing we were discussing. Hmm. What happens if i say (-1) ** (0.5+0j)? Ah, i get the right answer. Well, that's handy - it means i don't have to resort to cmath or sprinkle complex() calls all over the place for complex maths. tom -- Biochemistry is the study of carbon compounds that wriggle. -- http://mail.python.org/mailman/listinfo/python-list
