Q:

Bayesian R Programming

binomial <- function(nmax = 100,        
   thr = 0.95,                               
   alpha = 1,
   beta = 1,
   p_true = 0.5,
   p_0 = 0.5){

   for(j in seq.int(nmax, 0)){
      if(pbeta(q = p_0, shape1 = alpha + j, shape2 = beta + nmax - j, lower.tail = FALSE) < thr){
         targetatnmax <- j + 1
    } else {
    print(

         break
      }
   }
result <- list(Success = Success, targeratnmax = targetatnmax)
return(result)
}
res = binomial(nmax,thr,alpha,beta,p_true,p_0)
res

In my program I am trying to find the number of successes needed to exceed 0.95 thr. I am trying to use a for loop with if else statements but when I run it I don't get the value I need. I know my value should be 59 but I cannot seem to get this. I know the code seems really messy but its only because I have been playing around with it for hours. PLEASE ANY HELP

A:

Here is your code after clean-up:
binomial <- function(nmax = 100,        
                     thr = 0.95,                               
                     alpha = 1,
                     beta = 1,
                     p_true = 0.5,
                     p_0 = 0.5){
  targetatnmax <- 0

  for(j in seq.int(0,nmax)){
    if(pbeta(q = p_0, shape1 = alpha + j, shape2 = beta + nmax - j, lower.tail = FALSE) < thr){
      targetatnmax <- j + 1
    } else {      
        break
    }
  }
  result <- list(targeratnmax = targetatnmax)
  return(result)
}
res = binomial()
res

#$targeratnmax
#[1] 59

The main problem (other than the syntax errors and not existent objects) was that your loop ran from  nmax to 0 instead of the other way arround.
There is probably potential for optimization, but my understanding of the statistics is not good enough to really tackle that.

