[R] multiplication question

Moshe Olshansky m_olshansky at yahoo.com
Tue Jul 8 00:54:12 CEST 2008


The answer to your first question is 
sum(x)8sum(y) - sum(x*y)

and for the second one

x %*% R %*% y - sum(x*y*diag(R))


--- On Thu, 3/7/08, Murali Menon <feanor0 at hotmail.com> wrote:

> From: Murali Menon <feanor0 at hotmail.com>
> Subject: [R] multiplication question
> To: r-help at stat.math.ethz.ch
> Received: Thursday, 3 July, 2008, 2:30 AM
> 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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