R Help For Martingale Simulation

Question

I\'m trying to make a martingale simulation in R where I bet an amount and if I win I bet the same amount but if I lose, I bet double the amount. I do this until I run out of mo

Answer 1

Errors:

• Line 13: shouldn't be runif(1) = p, perhaps you meant runif(1) < p?
• Line 15: I suspect you meant amount_bet <- c instead of amount_bet <- amount_bet
• Line 21: should be i==100 not i=100
• Line 26: } should be moved before return() line

Things that don't affect execution of code, but should be changed:

• Line 16: it's good programming practice to write } else { one one line
• Line 24: you should move return() to its own line

Also, I'm not sure why there are two for loops. It seems like you only need one.

---

Here's my re-write of your code (with some assumptions about exactly what you're trying to do):

# write betting function
martingale <- function(m, c, p) {
    money   <- m
    betsize <- c
    i <- 1
    while(money > 0 & i <= 100) {
        if(runif(1) < p) {
            money <- money + betsize
            betsize <- c
        } else {
            money <- money - betsize
            betsize <- betsize * 2
        }
        i <- i + 1
    }
    return(money)
}

# run it 100 times
n <- 100
res_df <- data.frame(iteration = rep(NA_integer_, n), amountleft = rep(NA_real_, n))
for (i in 1:n) {
    res_df[i , "iteration"]  <- i
    res_df[i , "amountleft"] <- martingale(m=650, c=5, p=18/38)
}

Answer 2

Check out the line where you write:

if(runif(1) = p){}

Shouldn't that be a double equals sign?