let () =
  Printf.printf "Hello from rank %d of %d.\n" Parallel.rank Parallel.size;
  let () = Parallel.barrier () in
(*
let v = Parallel.Vec.init 47 (fun i -> float_of_int i) in
*)
  let a = Array.init 47 (fun i -> float_of_int (i+1)) in
  let v = Parallel.Vec.of_array a in
  Format.printf "%a" Parallel.Vec.pp v;