R小程序悬赏求助

求助 牛顿—拉弗森算法的R程序，希望高人帮忙写出来。谢了。

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)
}
}