for example ...
x <- 1:5 ; y<- 6:8
(m <- x %o% y)   # is this what you mean by product of two vectors?
sum(m[row(m)!=col(m)])   # or ...
sum(m)-sum(diag(m))

On Wed, Jul 2, 2008 at 7:30 PM, Murali Menon <feanor0@hotmail.com> wrote:

>
> folks,
>
> is there a clever way to compute the sum of the product of two vectors such
> that the common indices are not multiplied together?
>
> i.e. if i have vectors X, Y, how can i compute
>
> Sum  (X[i] * Y[j])
> i != j
>
> where i != j
>
> also, what if i wanted
>
> Sum (X[i] * Y[j] * R[i, j])
> i != j
>
> where R is a matrix?
>
> thanks,
>
> murali
>
>
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