# [R] problem with matrix multiplication

Huntsinger, Reid reid_huntsinger at merck.com
Wed May 23 20:06:00 CEST 2001

```You could do rep(Y,rep(n,p))*X. The outer "rep" expands Y by replacing each
entry with a number of copies determined by the corresponding entry in the
second argument. Here the second argument is rep(n,p) so the number of
copies is always n.

Reid Huntsinger

-----Original Message-----
From: Marlene Mueller [mailto:Marlene.Mueller at gmx.de]
Sent: Wednesday, May 23, 2001 1:10 PM
To: r-help at stat.math.ethz.ch
Subject: [R] problem with matrix multiplication

Hi, I look for a solution to the following problem:

I have a (n x p) matrix X and a (p x 1) vector Y which
are to be multiplied such the result is the (n x p) matrix

Z = ( X[,1]*Y[1] .... X[,p]*Y[p] )

Up to now I found that  sweep(X,2,Y,"*")  is (almost) what
I want, but only for p>1.

Is there another elegant way to do this by matrix
operations -- including the case p=1?

--
Marlene Mueller
http://www.uni-bayreuth.de/departments/math/org/mathe7/Mueller.html
http://ise.wiwi.hu-berlin.de/~marlene
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.
-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._.
_._
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

```