Running a Monte Carlo simulation in R, and building a vector from it

Question

The goal of the function I am trying to write is to do the following

1. Randomly choose a number N between 0 and 10.
2. Evaluate eq(N) = P.
3. Generate a number L randomly between 0 and 1.
4. If L > P, we discard this number, but otherwise, we add P to a vector of numbers.
5. Repeat this a number of times equal to runs, the input of our function.

Trying to run neutronrejector leads to several errors though:

Error: unexpected '=' in:
"  U <- U+1
  if(U ="
>   }
Error: unexpected '}' in "  }"
> }
Error: unexpected '}' in "}"

Those are the error messages. My code is below. Could anyone take a look at this and see what I am doing wrong? I am completely new to writing functions in R, I am more used to using preset packages.

eq = function(x){x*(exp(-x/1.4))}

values <- c()
U <- 0


neutronrejector = function(runs){
  repeat{
  N = runif(1, min=0, max=10)
  P = eq(N)
  L = runif(100, min=0, max=1)  
  ifelse(L > P, , values = c(N, values))
  U = U+1
  if(U = runs) break
  }
}

Answer 1

A few corrections:

• equality is tested by ==
• use runif(1,min=0,max=1) to get one random number
• if statement instead of ifelse

neutronrejector = function(runs){
  repeat{
    N = runif(1, min=0, max=10)
    P = eq(N)
    L = runif(1, min=0, max=1)  
    if (L > P) values = c(N, values)
    U = U+1
    if(U == runs) break
  }
  values
}

neutronrejector(10)
[1] 4.997457 7.699111 7.009196 5.515345 3.422422 9.495239 8.758963 2.209809 6.392655