Exponential regression -- incorrect case

[andiejs]

Hello, my example cases for exponential regression are giving incorrect results. Would it be possible for someone to check the algorithm on this? (Wolfram alpha gives correct results on this data, so this failure shouldn't be inevitable.) Thank you!

let test_exp () =
  let x = Owl.Mat.uniform 50 1 in
  let a = 14.8494 in
  let l = -4.21473 in
  let b = 0. in
  let y = Owl.Mat.((a $* exp (-.l $* x)) +$ b) in
  let a', l', b' = Owl.Regression.D.exponential x y in
  Printf.printf "(%g, %g, %g) (%g, %g, %g)\n" a l b a' l' b'
   (* (14.8494, -4.21473, 0) (1.48675e-46, 3.03379e-16, 238.706) *)

[andiejs]

This algorithm seems to work:
https://stackoverflow.com/a/61288871