numpy-discussion

[Numpy-discussion] scalar object bug or feature?

[Christopher H. <ch...@st...>]

Greetings,

I can't decide if the following is a bug or feature.  Numpy scalars are 
allowed to overflow silently while numarray upcasts to a larger python 
type.  I guess my biggest problem is that the overflow occurs silently.

In any case, is this known and expected behavior?

Thanks,
Chris



NUMARRAY example:

In [1]: import numarray as n

In [2]: a = n.array([2200,14000],type=n.UInt32)

In [3]: a0= a[0]

In [4]: a1 = a[1]

In [5]: adiff = a0-a1

In [6]: print a0,a1,adiff
2200 14000 -11800

In [7]: print type(a0),type(a1),type(adiff)
<type 'long'> <type 'long'> <type 'long'>

NUMPY example:
In [1]: import numpy as n

In [2]: a = n.array([2200,14000],dtype=n.uint32)

In [3]: a0= a[0]

In [4]: a1 = a[1]

In [5]: adiff = a0-a1

In [6]: print a0,a1,adiff
2200 14000 4294955496

In [7]: print type(a0),type(a1),type(adiff)
<type 'numpy.uint32'> <type 'numpy.uint32'> <type 'numpy.uint32'>

Re: [Numpy-discussion] scalar object bug or feature?

[Keith G. <kwg...@gm...>]

On 10/18/06, Christopher Hanley <ch...@st...> wrote:
> I can't decide if the following is a bug or feature.  Numpy scalars are
> allowed to overflow silently while numarray upcasts to a larger python
> type.  I guess my biggest problem is that the overflow occurs silently.

I had that problem yesterday, which was difficult to diagnose for a
new user like me.

Here's an example:

>> x = zeros((300, 300))
>> x = x > 1   # False
>> x = 1 - x    # ones
>> y = x.T * x
>> y[0,0]
44

Re: [Numpy-discussion] scalar object bug or feature?

[Alan G I. <ai...@am...>]

On Wed, 18 Oct 2006, Keith Goodman apparently wrote:=20
> Here's an example:=20
>>> x =3D zeros((300, 300))=20
>>> x =3D x > 1   # False=20
>>> x =3D 1 - x    # ones=20
>>> y =3D x.T * x=20
>>> y[0,0]=20
> 44=20


Here's a simpler (?) example:
>>> x=3Dnumpy.random.rand(300,1)>0
>>> x.sum()
300
>>> sum(x)
array([44], dtype=3Dint8)
>>> x=3Dnumpy.random.rand(300)>0
>>> sum(x)
300

Alan Isaac

Re: [Numpy-discussion] scalar object bug or feature?

[Charles R H. <cha...@gm...>]

On 10/18/06, Alan G Isaac <ai...@am...> wrote:
>
> On Wed, 18 Oct 2006, Keith Goodman apparently wrote:


<snip>

Here's a simpler (?) example:
> >>> x=numpy.random.rand(300,1)>0
> >>> x.sum()
> 300
> >>> sum(x)
> array([44], dtype=int8)
> >>> x=numpy.random.rand(300)>0
> >>> sum(x)
> 300
>
> Alan Isaac


Hmmm, I think sum(x) and x.sum() should behave the same. Note that

In [12]:sum(x, dtype=int)
Out[12]:300

I think sum should stick to the modular arithmetic unless specified
otherwise. But in any case sum(x) and x.sum() should do the same thing.

Chuck