Re: Matrix multiplication

["Richard M. Heiberger" <rmh@temple.edu>]

## The most efficient way to multiply two matrixes in S is to
## use the matrix multiplication function directly.

a <- matrix(runif(100000), 50000, 2)
b <- c(10, 20)
date()
P <- a %*% b
date()

## This takes less than 1 second


## Do it 1000 times:
date()
for (i in 1:1000)
   P <- a %*% b
date()
## This loop takes 26 seconds, or .026 seconds for each multiplication.

Rich