[Numpy-discussion] performance issue (again)

Mathew Yeates myeates@jpl.nasa....
Tue Apr 21 18:41:25 CDT 2009


sheer genius. Done in the blink of an eye and my original was taking 20 
minutes!


Keith Goodman wrote:
> On 4/21/09, Mathew Yeates <myeates@jpl.nasa.gov> wrote:
>   
>> Hi
>> I posted something about this earlier
>>
>> Say I have 2 arrays X and Y with shapes (N,3) where N is large
>> I am doing the following
>>
>> for row in range(N):
>>     result=polyfit(X[row,:],Y[row,:],1,full=True) # fit 3 points with a line
>>
>> This takes forever and I was hoping to find a way to speed things up.
>> But now I'm starting to wonder if this pointless. If the routine "poly
>> fit takes a  long time, when compared with the time for a Python
>> function call, then things can't be sped up.
>>
>> Any comments?
>>     
>
> If you remove the mean from x and y (along axis = 1) then can't you
> just do something like
>
> (x*y).sum(1) / (x*x).sum(axis=1)
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