[Numpy-discussion] bug in oldnumeric.ma

[Anne Archibald]

2008/5/7 Pierre GM <pgmdevlist@gmail.com>:
> On Wednesday 07 May 2008 20:38:22 Anne Archibald wrote:
>  > 2008/5/7 Pierre GM <pgmdevlist@gmail.com>:
>  > > All,
>  > >  Yes, there is a problem with ma.power: masking negative data should be
>  > >  restricted to the case of an exponent between -1. and 1. only, don't you
>  > >  think ?
>  >
>  > No, there's a problem with any fractional exponent (with even
>  > denominator): x**(3/2) == (x**3)**(1/2).
>
>  Argh. Good point.
>
>
>  > The real
>  > problem is "how do we predict when power() is going to produce a NaN?"
>   An alternative would be to forget about it: let power() output NaNs, and fix
>  them afterwards with fix_invalid.

Tempting, but the user may have used seterr() to arrange that
exceptions are raised when this happens, which is going to put a
spanner in the works.

(And temporarily changing seterr() is problematic in a multithreaded context...)

Anne