danhper · April 11, 2018 08:42
diff --git a/parmap_sample.ml b/parmap_sample.ml
 (**************************************************************************)
 (* Sample usage of OCaml parmap library                                   *)
 (* https://github.com/rdicosmo/parmap                                     *)
 (*                                                                        *)
 (* Computes pi using a simple approximation                               *)
 (* \frac{\pi}{4} = \sum_{n=0}^{\infty} \frac{(-1)^n}{2n + 1}              *)
 (*                                                                        *)
 (* Compile with the following command:                                    *)
 (* ocamlfind ocamlopt -linkpkg -package parmap parmap_sample.ml           *)
 (**************************************************************************)


 let compute_pi start stop =
  let rec loop n sum =
    if n >= stop then sum
    else
      let v = float (1 - (n mod 2) * 2) /. float (2 * n + 1) in
      loop (n + 1) (sum +. v)
  in
  4. *. (loop start 0.)

 let () =
  let max_val = 10000000000 in
  let nproc = Parmap.get_default_ncores () in
  let step = max_val / nproc in
  let parts = Array.mapi (fun i v -> i * step) (Array.init nproc (fun x -> x)) in
  let parts_seq = Parmap.A parts in
  let results = Parmap.parmap (fun v -> compute_pi v (v + step - 1)) parts_seq in
  let pi = List.fold_left ((+.)) 0. results in
  print_endline (string_of_float pi)
	(**************************************************************************)
	(* Sample usage of OCaml parmap library *)
	(* https://github.com/rdicosmo/parmap *)
	(* *)
	(* Computes pi using a simple approximation *)
	(* \frac{\pi}{4} = \sum_{n=0}^{\infty} \frac{(-1)^n}{2n + 1} *)
	(* *)
	(* Compile with the following command: *)
	(* ocamlfind ocamlopt -linkpkg -package parmap parmap_sample.ml *)
	(**************************************************************************)


	let compute_pi start stop =
	let rec loop n sum =
	if n >= stop then sum
	else
	let v = float (1 - (n mod 2) * 2) /. float (2 * n + 1) in
	loop (n + 1) (sum +. v)
	in
	4. *. (loop start 0.)

	let () =
	let max_val = 10000000000 in
	let nproc = Parmap.get_default_ncores () in
	let step = max_val / nproc in
	let parts = Array.mapi (fun i v -> i * step) (Array.init nproc (fun x -> x)) in
	let parts_seq = Parmap.A parts in
	let results = Parmap.parmap (fun v -> compute_pi v (v + step - 1)) parts_seq in
	let pi = List.fold_left ((+.)) 0. results in
	print_endline (string_of_float pi)