[Numpy-discussion] Pow() with negative exponent

[Ivan Vilata i Balaguer]

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
	                          ""

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