Loop structure for basic simulation model in R

问题

I'm trying to write a basic model that simulates the growth of a population (whose initial size is drawn randomly from a normal distribution) and then grows by a user defined amount each 'year' (currently 2 individuals in the code below for arguments sake). The output that is produced only shows the results of one simulation and, within this simulation, the population hasn't grown at all i.e. for each 'year' the population hasn't grown/doesn't add to the previous 'years' population. I'm assuming that I've stuffed something up in the loop structure and keen for any advice!

n.years <- 3
n.sim <- 5
store.growth <- matrix(ncol=3,nrow= (n.years * n.sim))

for (i in 1:n.sim) {
 init.pop.size <- rnorm(1,100,10)
 for (j in 1:n.years){
    #grow population
    grow.pop <- init.pop.size + 5
    store.growth[j,] <- cbind(grow.pop, n.years, n.sim)
 }
}
store.growth

来源：https://stackoverflow.com/questions/17101738/loop-structure-for-basic-simulation-model-in-r