About iteration count for recursive function-CodePudding

I am trying to write out the bisection function (

shows the iteration number is 0, I donot know how i can debug it, thank you for any help.

CodePudding user response：

Modifications to itera inside a function are done in the function's environment, not in the global environment.

You could pass itera as parameter to the function so that each recursive call increments its value:

bisect <- function(f, lower, upper, tol, itera=1)
{
  mid <- (lower   upper)/2
  if(abs(f(mid)) < tol){
    output <- list(root = mid, f.root = f(mid), iter = itera, estim.prec = abs(f(mid)))
    return(output)
  }
  else{
    itera = itera   1
    if(f(mid) * f(lower) < 0){
      
      bisect(f, lower, mid, tol,itera)
    }
    else{
      
      bisect(f, mid, upper, tol,itera)
    }
  }
}
f <- function(x) {x^3 - 2*x - 1}
bisect(f,1,2,10^(-6))

$root
[1] 1.618034

$f.root
[1] -6.01767e-07

$iter
[1] 21

$estim.prec
[1] 6.01767e-07

Another option is to modify itera value in calling environment using <<- operator :

itera <- 1
bisect <- function(f, lower, upper, tol)
{
  mid <- (lower   upper)/2
  if(abs(f(mid)) < tol){
    output <- list(root = mid, f.root = f(mid), iter = itera, estim.prec = abs(f(mid)))
    return(output)
  }
  else{
    itera <<- itera   1
    if(f(mid) * f(lower) < 0){
      
      bisect(f, lower, mid, tol)
    }
    else{
      
      bisect(f, mid, upper, tol)
    }
  }
}

$root
[1] 1.618034

$f.root
[1] -6.01767e-07

$iter
[1] 21

$estim.prec
[1] 6.01767e-07


f <- function(x) {x^3 - 2*x - 1}
bisect(f,1,2,10^(-6))