R help - Feb 2010 - For and while in looping

I would like to solve a nonlinear eqn using newton method and here is the code:
 
library(numDeriv)
 
fprime <- function(z) 
{ alp  <- 2.0165;
  rho  <- 0.868;
 
# simplified expressions
  a      <- alp-0.5
  c1     <- sqrt(pi)/(gamma(alp)*(1-rho)^alp)
  c2     <- sqrt(rho)/(1-rho)
  t1     <- exp(-z/(1-rho))
  t2     <- (z/(2*c2))^a  
  bes1   <- besselI(z*c2,a) 
  t1bes1 <- t1*bes1  
  c1*t1bes1*t2
}
 
## Newton iteration
newton_gam <- function(z)
{ n   <- length(z)
  r   <- runif(n) 
  tol <- 1E-6
 
  for (i in 1:n)
  { # numerical intergration to find the cdf
    cdf[i]  <- integrate(fprime, lower = 0, upper = z[i])$val
    
    # Newton method
    z[i]    <- z[i] - (cdf[i] - r[i])/fprime(z[i])
  }
  z
}
 
z <- c(0.5,10,20,30)
newton_gam(z)
 
Output
> z <- c(0.5,10,20,30)
 
> newton_gam(z)
[1]  4.498542e-01 -2.543392e+01 -4.031082e+03 -5.227064e+05
 
My question is how do I use ‘for’ and ‘while’ statement so that I can ask it to
repeat until it reaches certain tolerance and for a certain number of times.
Thank you.


      
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