[R] Help vectorising a function

[hadley wickham]

M <- function(m, s, init = 0) {
	A <- nrow(m); T <- ncol(m)
	M <- matrix(init, nrow = A, ncol = T)

	for(a in 1:(A-1)) {
		M[a+1, 2:T] <- (s[a] * (M[a, ] + m[a, ]))[1:(T-1)]
	}
	M
}

This is from a mark-recapture study where M is an estimate of the
number of marked fish in each age class (A) over each year (T).  s is
a vector of age dependent survival probabilities and m is a matrix
containing the number of fish marked for the first time (in each age
class and year).

I'm pretty sure there's a much better way of doing this - but I can't
see it.  I'm not looking for the exact code to solve the problem -
just a better way of attacking it.  Any hints would be much
appreciated!

Hadley