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 <[EMAIL PROTECTED]> wrote: > From: Murali Menon <[EMAIL PROTECTED]> > Subject: [R] multiplication question > To: [EMAIL PROTECTED] > 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 > > > _________________________________________________________________ > Enter the Zune-A-Day Giveaway for your chance to win — > day after day after day > > M_Mobile_Zune_V1 > [[alternative HTML version > deleted]]______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, > reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
