inverse.egi

--
-- Inverse
--

inverse t f x :=
  match f as mathExpr with
    | ?isSimpleTerm ->
      match f as symbolExpr with
        | #x -> t
        | #exp #x -> log t
        | #log #x -> exp t
        | #sqrt #x -> t ^ 2
        | #cos #x -> acos t
        | #sin #x -> asin t
        | #acos #x -> cos t
        | #asin #x -> sin t
        | _ -> inverse' t f x  -- TODO: define inverse'
    | ?isTerm ->
      match f as termExpr with
        | term #1 (ncons $n #x []) -> rt n t
        | term _ (ncons $n #x _) ->
          let a := f / x ^ n
           in inverse (t / a) (f / a) x
        | _ -> `inverse t f x
    | ?isPolynomial ->
      match coefficients x f as list mathExpr with
        | $c :: (loop $i (1, $n)
                   (#0 :: ...)
                   ($a :: [])) -> inverse ((t - c) / a) (x ^ (n + 1)) x
        | _ -> `inverse t f x
    | _ ->
      match f as mathExpr with
        | $p1 / $p2 -> inverse (p2 * t) p1 x
    | _ -> `inverse t f x