[Numpy-discussion] Pow() with negative exponent

[Pujo Aji]

Numpy optimize the python process by explicitly define the element type of
array.
Just like C++.

Python let you work with automatic converting... but it slows down the
process.
Like having extra code to check the type of your element array.

I suggest you check the numpy reference instead of python reference when
using numpy.

Sincerely Yours,
pujo


On 5/23/06, Ivan Vilata i Balaguer <ivilata at carabos.com> wrote:
>
> En/na Pujo Aji ha escrit::
>
> > use 'f' to tell numpy that its array element is a float type:
> > b = numpy.array([1,2,3,4],'f')
> >
> > an alternative is to put dot after the number:
> > b = numpy.array([1. ,2. ,3. ,4.])
> >
> > This hopefully solve your problem.
>
> You're right, but according to Python reference docs, having an integer
> base and a negative integer exponent should still return a floating
> point result, without the need of converting the base to floating point
> beforehand.
>
> I wonder if the numpy/numarray behavior is based on some implicit policy
> which states that operating integers with integers should always return
> integers, for return type predictability, or something like that.  Could
> someone please shed some light on this?  Thanks!
>
> En/na Pujo Aji ha escrit::
>
> > On 5/23/06, *Ivan Vilata i Balaguer* <ivilata at carabos.com
> > <mailto:ivilata at carabos.com>> wrote:
> > [...]
> >     According to http://docs.python.org/ref/power.html:
> >
> >       For int and long int operands, the result has the same type as the
> >       operands (after coercion) unless the second argument is negative;
> in
> >       that case, all arguments are converted to float and a float result
> is
> >       delivered.
> >
> >     Then, shouldn't be ``b ** -1 == array([1.0, 0.5, 0.33333333, 0.25
> ])``
> >     (i.e. a floating point result)? Is this behaviour intentional?  (I
> >     googled for previous messages on the topic but I didn't find any.)
>
> ::
>
>         Ivan Vilata i Balaguer   >qo<   http://www.carabos.com/
>                Cárabos Coop. V.  V  V   Enjoy Data
>                                   ""
>
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/numpy-discussion/attachments/20060523/04efb1f5/attachment.html>