问用于MLE的Newton Raphson代码-需要TRUE/FALSE的缺失值

EN

newtonraphson <- function(ftn, x0, tol = 1e-9, max.iter = 100) {
 x <- x0
 fx <- ftn(x)     
 iter <- 0
 while ((abs(fx[1]) > tol) & (iter < max.iter)) {
  x <- x - fx[1]/fx[2]
  fx <- ftn(x)
  iter <- iter + 1
  cat("At iteration", iter, "value of x is:", x, "\n")
 }
 if (abs(fx[1]) > tol) {
  cat("Algorithm failed to converge\n")
  return(NULL)}
  else {
  cat("Algorithm converged\n")
  return(x)}
}

X <- c(3,1,2,0,6,8,4,5,7,0)    
n <- 10
lambda <- seq(0,10,0.01)
ftn <- function(p) {
 for (i in 1:10){
 fp <- sum(X[i])*log(lambda) - 10*lambda
 dfp <- (1/lambda)*sum(X[i]) - 10
 }
 return(c(fp,dfp))
}

newtonraphson(ftn, 0.1, 1e-06)

Error in while ((abs(fx[1]) >= tol) & (iter <= max.iter)) { : 
missing value where TRUE/FALSE needed