[Numpy-discussion] bug in round with negative number of decimals

[Charles R Harris]

On 9/4/06, Sebastian Haase <haase at msg.ucsf.edu> wrote:
>
> Paulo J. S. Silva wrote:
> > Once again, the information that singed zero is part of IEEE standard is
> > in the paper I cited in my last message.
> >
> > It is very important to be able to compute the sign of an overflowed
> > quantity in expressions like 1/x when x goes to zero.
> >
> > Best,
> >
> > Paulo
> Hi,
>
> This is all very interesting ( and confusing (to me, maybe others) at
> the same time ...) ...
>
> Question 0: Are you sure this is not a bug ?
>   >>> N.array([66]).round(-1)
> [60]


That does look like a bug.

>>> array([66]).round(-1)
array([60])
>>> array([66.]).round(-1)
array([ 70.])

I suspect it is related to the integer data type of the first example. The
code probably does something like this:

round(66/10)*10

and 66/10 == 6 in integer arithmetic.

Chuck


  >>> N.array([66.2]).round(-1)
> [ 70.]
>
> Question 1: Was this way of round already in Numeric and /or in numarray ?


Don't recall.

Question 2: Does this need to be better documented (complete and
> corrected(!) docstrings - maybe a dedicated wiki page )  !?
> This is related to "How does Matlab or IDL or others do rounding ?" -
> This would at least determine how many people would be surprised by this.
> (I would say that *if* Matlab rounds the same way, we might need less
> documentation ...)


I have improved the document strings and the example at scipy.org.

Chuck
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