type complex = {
    mutable x : float;
    mutable y : float;
  }

let iters1 max_iter xc yc =
  let c = { x=xc; y=yc } in
  let rec aux count =
    if count = max_iter then max_iter else begin
      if c.x *. c.x  +. c.y *. c.y >= 4.0 then count else begin
        let x = c.x in
        c.x <- x *. x -. c.y *. c.y +. xc;
        c.y <- 2.0 *. x *. c.y +. yc;
        aux (count+1)
      end
    end in
  aux 0