matrix program

I'm attempting to produce a program in which i can multiply a 4x4
matrix by a vector.  I would like to have this occur 30 times with the
product of the matrix and vector replace the original vector, kind of
like population growth. I'm having difficulties with the programing
aspect and continuously get errors from R.  I would appreciate any
help.

Are you looking for something like this toy example?

Generate a matrix mm and a vector xx:

R> mm <- matrix(rep(1, 4), ncol = 2)
R> xx <- rep(1, 2)
R> mm
     [,1] [,2]
[1,]    1    1
[2,]    1    1
R> xx
[1] 1 1

And then pre-multiply 10 times by mm:

R> for(i in 1:10) xx <- mm %*% xx
R> xx
     [,1]
[1,] 1024
[2,] 1024

which in this case is of course just 2^10.

hth,
Z

Owen Buchner