[Numpy-discussion] performance issue (again)

Keith Goodman kwgoodman@gmail....
Tue Apr 21 17:23:11 CDT 2009

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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