[Numpy-discussion] Fast vector multiplication

Mark Janikas mjanikas at esri.com
Fri Jan 19 17:04:52 CST 2007

Doh!!!  Nice call.  Thanks for the input.





From: numpy-discussion-bounces at scipy.org
[mailto:numpy-discussion-bounces at scipy.org] On Behalf Of Timothy
Sent: Friday, January 19, 2007 2:52 PM
To: Discussion of Numerical Python
Subject: Re: [Numpy-discussion] Fast vector multiplication



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.




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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