Average Error: 13.5 → 0.3
Time: 1.0m
Precision: 64
Internal Precision: 832
\[wj - \frac{wj \cdot e^{wj} - x}{e^{wj} + wj \cdot e^{wj}}\]
\[\begin{array}{l} \mathbf{if}\;wj \le -8.379297298080333 \cdot 10^{-09} \lor \neg \left(wj \le 4.7290331869132735 \cdot 10^{-09}\right):\\ \;\;\;\;\left(wj - \frac{1}{(wj \cdot wj + -1)_*} \cdot \left(\left(wj - 1\right) \cdot wj\right)\right) - \frac{\frac{wj + -1}{(wj \cdot wj + -1)_*}}{\frac{e^{wj}}{-x}}\\ \mathbf{else}:\\ \;\;\;\;(wj \cdot \left((x \cdot -2 + wj)_*\right) + x)_*\\ \end{array}\]

Error

Bits error versus wj

Bits error versus x

Target

Original13.5
Target12.9
Herbie0.3
\[wj - \left(\frac{wj}{wj + 1} - \frac{x}{e^{wj} + wj \cdot e^{wj}}\right)\]

Derivation

  1. Split input into 2 regimes
  2. if wj < -8.379297298080333e-09 or 4.7290331869132735e-09 < wj

    1. Initial program 15.2

      \[wj - \frac{wj \cdot e^{wj} - x}{e^{wj} + wj \cdot e^{wj}}\]
    2. Using strategy rm
    3. Applied distribute-rgt1-in15.3

      \[\leadsto wj - \frac{wj \cdot e^{wj} - x}{\color{blue}{\left(wj + 1\right) \cdot e^{wj}}}\]
    4. Applied *-un-lft-identity15.3

      \[\leadsto wj - \frac{\color{blue}{1 \cdot \left(wj \cdot e^{wj} - x\right)}}{\left(wj + 1\right) \cdot e^{wj}}\]
    5. Applied times-frac15.3

      \[\leadsto wj - \color{blue}{\frac{1}{wj + 1} \cdot \frac{wj \cdot e^{wj} - x}{e^{wj}}}\]
    6. Simplified3.2

      \[\leadsto wj - \frac{1}{wj + 1} \cdot \color{blue}{\left(wj - \frac{x}{e^{wj}}\right)}\]
    7. Using strategy rm
    8. Applied flip-+3.4

      \[\leadsto wj - \frac{1}{\color{blue}{\frac{wj \cdot wj - 1 \cdot 1}{wj - 1}}} \cdot \left(wj - \frac{x}{e^{wj}}\right)\]
    9. Applied associate-/r/3.3

      \[\leadsto wj - \color{blue}{\left(\frac{1}{wj \cdot wj - 1 \cdot 1} \cdot \left(wj - 1\right)\right)} \cdot \left(wj - \frac{x}{e^{wj}}\right)\]
    10. Applied associate-*l*3.3

      \[\leadsto wj - \color{blue}{\frac{1}{wj \cdot wj - 1 \cdot 1} \cdot \left(\left(wj - 1\right) \cdot \left(wj - \frac{x}{e^{wj}}\right)\right)}\]
    11. Simplified3.3

      \[\leadsto wj - \color{blue}{\frac{1}{(wj \cdot wj + -1)_*}} \cdot \left(\left(wj - 1\right) \cdot \left(wj - \frac{x}{e^{wj}}\right)\right)\]
    12. Using strategy rm
    13. Applied sub-neg3.3

      \[\leadsto wj - \frac{1}{(wj \cdot wj + -1)_*} \cdot \left(\left(wj - 1\right) \cdot \color{blue}{\left(wj + \left(-\frac{x}{e^{wj}}\right)\right)}\right)\]
    14. Applied distribute-rgt-in3.3

      \[\leadsto wj - \frac{1}{(wj \cdot wj + -1)_*} \cdot \color{blue}{\left(wj \cdot \left(wj - 1\right) + \left(-\frac{x}{e^{wj}}\right) \cdot \left(wj - 1\right)\right)}\]
    15. Applied distribute-rgt-in3.3

      \[\leadsto wj - \color{blue}{\left(\left(wj \cdot \left(wj - 1\right)\right) \cdot \frac{1}{(wj \cdot wj + -1)_*} + \left(\left(-\frac{x}{e^{wj}}\right) \cdot \left(wj - 1\right)\right) \cdot \frac{1}{(wj \cdot wj + -1)_*}\right)}\]
    16. Applied associate--r+3.3

      \[\leadsto \color{blue}{\left(wj - \left(wj \cdot \left(wj - 1\right)\right) \cdot \frac{1}{(wj \cdot wj + -1)_*}\right) - \left(\left(-\frac{x}{e^{wj}}\right) \cdot \left(wj - 1\right)\right) \cdot \frac{1}{(wj \cdot wj + -1)_*}}\]
    17. Simplified3.3

      \[\leadsto \left(wj - \left(wj \cdot \left(wj - 1\right)\right) \cdot \frac{1}{(wj \cdot wj + -1)_*}\right) - \color{blue}{\frac{\frac{wj + -1}{(wj \cdot wj + -1)_*}}{\frac{e^{wj}}{-x}}}\]

    if -8.379297298080333e-09 < wj < 4.7290331869132735e-09

    1. Initial program 13.4

      \[wj - \frac{wj \cdot e^{wj} - x}{e^{wj} + wj \cdot e^{wj}}\]
    2. Taylor expanded around 0 0.1

      \[\leadsto \color{blue}{\left({wj}^{2} + x\right) - 2 \cdot \left(x \cdot wj\right)}\]
    3. Simplified0.2

      \[\leadsto \color{blue}{(wj \cdot \left((x \cdot -2 + wj)_*\right) + x)_*}\]
  3. Recombined 2 regimes into one program.
  4. Final simplification0.3

    \[\leadsto \begin{array}{l} \mathbf{if}\;wj \le -8.379297298080333 \cdot 10^{-09} \lor \neg \left(wj \le 4.7290331869132735 \cdot 10^{-09}\right):\\ \;\;\;\;\left(wj - \frac{1}{(wj \cdot wj + -1)_*} \cdot \left(\left(wj - 1\right) \cdot wj\right)\right) - \frac{\frac{wj + -1}{(wj \cdot wj + -1)_*}}{\frac{e^{wj}}{-x}}\\ \mathbf{else}:\\ \;\;\;\;(wj \cdot \left((x \cdot -2 + wj)_*\right) + x)_*\\ \end{array}\]

Runtime

Time bar (total: 1.0m)Debug logProfile

herbie shell --seed 2018235 +o rules:numerics
(FPCore (wj x)
  :name "Jmat.Real.lambertw, newton loop step"

  :herbie-target
  (- wj (- (/ wj (+ wj 1)) (/ x (+ (exp wj) (* wj (exp wj))))))

  (- wj (/ (- (* wj (exp wj)) x) (+ (exp wj) (* wj (exp wj))))))