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Source file owl_base_maths.ml

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# 1 "src/base/maths/owl_base_maths.ml"
(*
 * OWL - OCaml Scientific and Engineering Computing
 * Copyright (c) 2016-2020 Liang Wang <liang.wang@cl.cam.ac.uk>
 *)

let add x y = x +. y

let sub x y = x -. y

let mul x y = x *. y

let div x y = x /. y

let pow x y = x ** y

let fmod x y = Stdlib.mod_float x y

let atan2 x y = Stdlib.atan2 x y

let hypot x y = Stdlib.hypot x y

let abs x = Stdlib.abs_float x

let neg x = ~-.x

let reci x = 1. /. x

let softsign x = x /. (1. +. abs x)

let softplus x = log (1. +. exp x)

let sqr x = x *. x

let sqrt x = Stdlib.sqrt x

let cbrt x = x ** 0.33333333333333333333

let exp x = Stdlib.exp x

let exp2 x = 2. ** x

let exp10 x = 10. ** x

let expm1 x = Stdlib.expm1 x

let log x = Stdlib.log x

let log2 x = log x /. Owl_const.loge2

let log10 x = Stdlib.log10 x

let log1p x = Stdlib.log1p x

let signum x =
  if FP_nan = classify_float x
  then nan
  else if x > 0.
  then 1.
  else if x < 0.
  then ~-.1.
  else 0.


let floor x = Stdlib.floor x

let ceil x = Stdlib.ceil x

let round x = floor (x +. 0.5)

let trunc x = modf x |> snd

let fix x = if x < 0. then ceil x else floor x

let sin x = Stdlib.sin x

let cos x = Stdlib.cos x

let tan x = Stdlib.tan x

let cot x = 1. /. tan x

let sec x = 1. /. cos x

let csc x = 1. /. sin x

let sinh x = Stdlib.sinh x

let cosh x = Stdlib.cosh x

let tanh x = Stdlib.tanh x

let asin x = Stdlib.asin x

let acos x = Stdlib.acos x

let atan x = Stdlib.atan x

let acot x = (Owl_const.pi /. 2.) -. atan x

let asec x = Stdlib.acos (1. /. x)

let acsc x = Stdlib.asin (1. /. x)

let asinh x = log (x +. sqrt ((x *. x) +. 1.))

let acosh x = log (x +. sqrt ((x *. x) -. 1.))

let atanh x = 0.5 *. log ((1. +. x) /. (1. -. x))

let acoth x = atanh (1. /. x)

let asech x = acosh (1. /. x)

let acsch x = asinh (1. /. x)

let relu x = Stdlib.max 0. x

let dawsn _x = raise (Owl_exception.NOT_IMPLEMENTED "Owl_base_maths.dawsn")

let sigmoid x = 1. /. (1. +. log ~-.x)

let xlogy x y = if x = 0. && classify_float y <> FP_nan then 0. else x *. log y

let xlog1py x y = if x = 0. && classify_float y <> FP_nan then 0. else x *. log1p y

let logit x = log (x /. (1. -. x))

let expit x = 1. /. (1. +. exp (-.x))

let log1mexp x = if -.x > log 2. then log1p (-.exp x) else log (-.expm1 x)

let log1pexp x =
  if x <= -37.
  then exp x
  else if x <= 18.
  then log1p (exp x)
  else if x <= 33.3
  then x +. exp (-.x)
  else x


let erf x =
  let a = 0.254829592 in
  let b = -0.284496736 in
  let c = 1.421413741 in
  let d = -1.453152027 in
  let e = 1.061405429 in
  let p = 0.327591100 in
  let sign = signum x in
  let x = abs x in
  let t = 1. /. (1. +. (p *. x)) in
  let y =
    1.
    -. (((((((((e *. t) +. d) *. t) +. c) *. t) +. b) *. t) +. a) *. t *. exp (-.x *. x))
  in
  sign *. y


let erfc x = 1. -. erf x

let erfcx x = exp (x *. x) *. erfc x

(* Helper functions *)

let is_nan x = FP_nan = classify_float x

let is_inf x = FP_infinite = classify_float x

let is_normal x = FP_normal = classify_float x

let is_subnormal x = FP_subnormal = classify_float x

let is_odd x = Stdlib.abs x mod 2 = 1

let is_even x = x mod 2 = 0

let is_pow2 x = x <> 0 && x land (x - 1) = 0

let same_sign x y =
  if x >= 0. && y >= 0. then true else if x <= 0. && y <= 0. then true else false


let is_simplex x =
  let acc = ref 0. in
  let chk = ref true in
  (try
     Array.iter
       (fun a ->
         if a < 0.
         then (
           chk := false;
           raise Owl_exception.FOUND);
         acc := !acc +. a)
       x
   with
  | _exn -> ());
  let df = abs_float (1. -. !acc) in
  if df > Owl_const.eps then chk := false;
  !chk


let is_int x = modf x |> fst |> ( = ) 0.

let is_sqr x = float_of_int x |> sqrt |> is_int

let _binary_exp a b m f id =
  let r = ref id in
  let a = ref a in
  let b = ref b in
  while !a > 0 do
    if !a land 1 = 1 then r := f !r !b m;
    a := !a lsr 1;
    if !a > 0 then b := f !b !b m
  done;
  !r


let mulmod a b m =
  let error () =
    let s =
      Printf.sprintf
        "mulmod requires a >= 0, b >= 0, m >= 1; however the inputs are a = %i, b = %i, \
         m = %i"
        a
        b
        m
    in
    Owl_exception.INVALID_ARGUMENT s
  in
  let predicate = a >= 0 && b >= 0 && m >= 1 in
  Owl_exception.verify predicate error;
  let a = a mod m in
  let b = b mod m in
  if a = 0 || b = 0
  then 0
  else if b < max_int / a
  then a * b mod m
  else (
    let _muladd a b m =
      let c = m - b in
      if a >= c then a - c else m - c + a
    in
    _binary_exp a b m _muladd 0)


let powmod a b m =
  let error () =
    let s =
      Printf.sprintf
        "powmod requires a >= 0, b >= 0, m >= 1; however the inputs are a = %i, b = %i, \
         m = %i"
        a
        b
        m
    in
    Owl_exception.INVALID_ARGUMENT s
  in
  let predicate = a >= 0 && b >= 0 && m >= 1 in
  Owl_exception.verify predicate error;
  if m = 1 && b = 0 then 0 else _binary_exp b (a mod m) m mulmod 1


let fermat_fact x =
  let s = "the input of fermat_fact should be an odd number" in
  Owl_exception.(check (is_odd x = true) (INVALID_ARGUMENT s));
  let x = float_of_int x in
  let y = ref (ceil (sqrt x)) in
  let z = ref ((!y *. !y) -. x) in
  while is_int (sqrt !z) = false do
    y := !y +. 1.;
    z := (!y *. !y) -. x
  done;
  let fac0 = !y +. sqrt !z |> int_of_float in
  let fac1 = !y -. sqrt !z |> int_of_float in
  fac0, fac1


let is_prime x =
  let _possible_prime s d n a =
    let p = ref (powmod a d n) in
    if !p = 1 || !p = n - 1
    then true
    else (
      let r = ref false in
      let _ =
        try
          for _ = 0 to s - 1 do
            p := mulmod !p !p n;
            if !p = n - 1 then raise Owl_exception.FOUND
          done
        with
        | _ -> r := true
      in
      !r)
  in
  let _factor_powtwo n =
    let i, r = ref 0, ref n in
    while !r land 1 = 0 do
      r := !r lsr 1;
      i := !i + 1
    done;
    !i, !r
  in
  if x < 30
  then Array.mem x [| 2; 3; 5; 7; 11; 13; 17; 19; 23; 29 |]
  else if x mod 2 = 0 || x mod 3 = 0
  then false
  else (
    let bases =
      (* bases from https://miller-rabin.appspot.com *)
      if x <= 1073741823
      then (* 2^30 - 1 *)
        [| 2; 7; 61 |]
      else [| 2; 325; 9375; 28178; 450775; 9780504; 6 * 299210837 |]
    in
    let s, d = _factor_powtwo (x - 1) in
    Array.for_all (fun b -> b mod x = 0 || _possible_prime s d x (b mod x)) bases)
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