[Numpy-discussion] performance issue (again)

josef.pktd@gmai... josef.pktd@gmai...
Tue Apr 21 17:41:12 CDT 2009


On Tue, Apr 21, 2009 at 6:23 PM, Keith Goodman <kwgoodman@gmail.com> 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)
>


I think that's what I said 8 days ago.

Josef
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