[Numpy-discussion] matrix problem: float to matrix power

Robert Kern robert.kern@gmail....
Wed Oct 31 12:01:15 CDT 2007


Charles R Harris wrote:
> On 10/31/07, Alan G Isaac <aisaac@american.edu> wrote:
>>>>> 1.0**numpy.array([1,2,3])
>> array([ 1.,  1.,  1.])
>>>>> 1.0**numpy.mat([1,2,3])
>> Traceback (most recent call last):
>>   File "<stdin>", line 1, in <module>
>> TypeError: unsupported operand type(s) for ** or pow(): 'float' and 'matrix'
>>
>> Why the restriction for matrices?
> 
> Looks like it just got overlooked. It works fine for 2D arrays.
> 
> In [11]: 1.0**eye(3)
> Out[11]:
> array([[ 1.,  1.,  1.],
>        [ 1.,  1.,  1.],
>        [ 1.,  1.,  1.]])

For ndarrays, it does elementwise exponentiation, so it is neither here nor
there with respect to matrices. What is the definition of a scalar raised to a
matrix power? I don't ever recall seeing one.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco


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