[Numpy-discussion] an array become a matrix after an element assignment

[Nathaniel Smith]

Happens to me all the time...

On Sat, Apr 16, 2011 at 8:51 PM, Forrest Sheng Bao
<forrest.bao at gmail.com> wrote:
> Oh yeah, my bad. Forget about it. I guess I was too tired.
>
> Cheers, Forrest
>
> On Sat, Apr 16, 2011 at 10:47 PM, Nathaniel Smith <njs at pobox.com> wrote:
>>
>> On Sat, Apr 16, 2011 at 8:39 PM, Forrest Sheng Bao
>> <forrest.bao at gmail.com> wrote:
>> >>>> a=zeros((3,3)) + eye(3)
>> >>>> a*a
>> > array([[ 1.,  0.,  0.],
>> >        [ 0.,  1.,  0.],
>> >        [ 0.,  0.,  1.]])
>> >
>> > Then i assigned a value to one of the element:
>> >
>> >>>> a[1,2]=4
>> >
>> > Finally, the '*' operator was interpreted as a matrix multiplication
>> >
>> >>>> a*a
>> > array([[  1.,   0.,   0.],
>> >        [  0.,   1.,  16.],
>> >        [  0.,   0.,   1.]])
>>
>> That looks like element-wise multiplication to me? (Matrix
>> multiplication would have given you an 8 where you have a 16.)
>>
>> -- Nathaniel
>
>