This comes up from time to time. The problem is that one needs complex
numbers to address taking the third root: there are three cube roots
for any nonzero number (real or complex). To wit:
> (-0.0841219200008394+0i)^(1/3)
[1] 0.2190818+0.3794609i
> (-0.0841219200008394-0i)^(1/3)
[1] 0.2190818+0.3794609i
> (-0.0841219200008394+1e-100i)^(1/3)
[1] 0.2190818+0.3794609i
> (-0.0841219200008394-1e-100i)^(1/3)
[1] 0.2190818-0.3794609i
>
Note the first two are identical but the second two differ.
Anyone care to start discussing signed zero again?
[you probably want the *real* cube root, in which case it
is best to take minus the unique real cube root of the absolute value:
> -(0.0841219200008394)^(1/3)
[1] -0.4381637
>
(which is what you did, of course!)]
HTH
rksh
Juan Manuel Barreneche wrote:
Well, this is what i got...
-0.0841219200008394^(1/3)
[1] -0.438163696867656
(-0.0841219200008394)^(1/3)
[1] NaN
and i don't have a clue of why this happens or how to avoid it, any suggestions?
thank you,
Juan
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