Average Error: 14.0 → 1.9
Time: 32.5s
Precision: 64
Internal Precision: 128
\[wj - \frac{wj \cdot e^{wj} - x}{e^{wj} + wj \cdot e^{wj}}\]
↓
\[(wj \cdot \left((x \cdot -2 + wj)_*\right) + x)_*\]

Error

Bits error versus wj

Bits error versus x

Target

Original14.0
Target13.5
Herbie1.9
\[wj - \left(\frac{wj}{wj + 1} - \frac{x}{e^{wj} + wj \cdot e^{wj}}\right)\]

Derivation

  1. Initial program 14.0

    \[wj - \frac{wj \cdot e^{wj} - x}{e^{wj} + wj \cdot e^{wj}}\]

  2. Initial simplification14.0

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

  3. Taylor expanded around 0 1.9

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

  4. Simplified1.9

    \[\leadsto \color{blue}{(wj \cdot \left((x \cdot -2 + wj)_*\right) + x)_*}\]

  5. Final simplification1.9

    \[\leadsto (wj \cdot \left((x \cdot -2 + wj)_*\right) + x)_*\]

Runtime

Time bar (total: 32.5s)Debug logProfile

herbie shell --seed 2018346 +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))))))