[R] multiplication question

From: Murali Menon <feanor0_at_hotmail.com>
Date: Wed, 02 Jul 2008 16:30:46 +0000


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?  



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