Serious bug with not_equal_scalar function always returning the wrong result.

[zoj613]

There is a serious bug with the implementation of not_equal_scalar function. In it's current state, it is an alias for equal_scalar since it returns the opposite of it's expected result. Here is a reproducing example:

module Ndarray = Owl.Dense.Ndarray.Generic;;
let x = Ndarray.create Bigarray.Int64 [|2;2;2|] 10L;;
Ndarray.equal_scalar x 10L;;
(*- : bool = true *)
Ndarray.not_equal_scalar x 10L;;
(*- : bool = true *)

Evidently, not_equal_scalar is supposed to return false. With the help of my LSP server, I was able to jump to the definition of this function and to my surprised found that the underlying implementation of both functions is identical. See:

owl/src/owl/dense/owl_dense_ndarray_generic.ml

Lines 1940 to 1942 in 455bde1

	let equal_scalar x a = _owl_equal_scalar (kind x) (numel x) x a = 1
	let not_equal_scalar x a = _owl_equal_scalar (kind x) (numel x) x a = 1

Basically the implementation of equal_scalar was copied over to not_equal_scalar. I looked to see if there is an implementation function named _not_equal_scalar and it turns out it does exist at:

owl/src/owl/core/owl_ndarray_maths.ml

Line 1618 in 455bde1

let _owl_not_equal_scalar : type a b. (a, b) kind -> (a, b) owl_arr_op10 = function

So a simple fix for this bug is to just replace

let not_equal_scalar x a = _owl_equal_scalar (kind x) (numel x) x a = 1 

with

let not_equal_scalar x a = _owl_not_equal_scalar (kind x) (numel x) x a = 1 

Cc @mseri @jzstark