model <- function(t, state, parms) {
  N <- state
  S <- A %*% N # R code for matrix x vector multiplication
  dN <- r*N*(1 - S)
  return(list(dN))  
}  

p <- c()
n <- 3
s <- rep(0.1,n)
names(s) <- paste("N",seq(1,n),sep="")
r <- abs(rnorm(n,1,0.1))
A <- matrix(runif(n*n),nrow=n,ncol=n)
diag(A) <- 1; A

run()