When do I have to set a seed?-CodePudding

I think this is a very basic question

I am doing simulations, so I make functions to recreate for example a random walk, which mathematically takes this form:

so to simulate it I make my function:

ar_1 <- function(iter, y0, sigma_e){
  
  e <- rnorm(iter, sd = sigma_e)
  
  y <- numeric(iter)
  y[1] <- y0
  
  for(t in 2:iter){
    y[t] = y[t-1] e[t]
  }
  
  result <- data.frame(iteration  = seq(1,iter), y = y)
  
  print(plot(result$iteration, result$y, type="l"))
  
  return(result)
}

try1 <- ar_1(iter = 100, y0 = 2, sigma_e = 0.0003)

So the thing is the e vector takes random numbers.

I want to replicate the same graph and values wherever, so I know I gotta use a seed.

So my question is: does the seed goes inside the function or at the very start of the script?

Furthermore, I would want to know why.

CodePudding user response：

If you set.seed once at the top of the script, the seed will remain set until the first call to rnorm. Subsequent calls to functions that require a random seed will not use the initial seed.

So really the answer is: do you intend to call the function more than once? If so, then set the seed inside the function.