[Numpy-discussion] Fast vector multiplication

Timothy Hochberg tim.hochberg at ieee.org
Fri Jan 19 16:51:51 CST 2007


On 1/19/07, Mark Janikas <mjanikas at esri.com> wrote:
>
>  Hello all,
>
>
>
> I am trying to figure out the most efficient way to get the sum of the
> product of two vectors where id != id.
>
>
>
> E.g.:
>
>
>
> X = array([1,2,3])
>
> Y = array([1,2,3])
>
>
>
> Z = (1*2) + (1*3) + (2*1) + (2*3) + (3*1) + (3*2) = 22
>
>
>
> I could obviously do this with loops, but I was wondering if there is a
> version of multiply that could be used… or a form of vectorize.  Any ideas
> would be greatly appreciated.
>

Isn't this just equivalent to:
sum(X) * sum(Y) - dot(X, Y)
?

If so, I would just use that.



-- 

//=][=\\

tim.hochberg at ieee.org
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