\[wj - \frac{wj \cdot e^{wj} - x}{e^{wj} + wj \cdot e^{wj}}\]
Test:
Jmat.Real.lambertw, newton loop step
Bits:
128 bits
Bits error versus wj
Bits error versus x
Time: 5.7 s
Input Error: 28.2
Output Error: 0.0
Log:
Profile: 🕒
\((\left(wj - 2 \cdot x\right) * wj + x)_*\)
  1. Started with
    \[wj - \frac{wj \cdot e^{wj} - x}{e^{wj} + wj \cdot e^{wj}}\]
    28.2
  2. Using strategy rm
    28.2
  3. Applied distribute-rgt1-in to get
    \[wj - \frac{wj \cdot e^{wj} - x}{\color{red}{e^{wj} + wj \cdot e^{wj}}} \leadsto wj - \frac{wj \cdot e^{wj} - x}{\color{blue}{\left(wj + 1\right) \cdot e^{wj}}}\]
    28.4
  4. Applied *-un-lft-identity to get
    \[wj - \frac{\color{red}{wj \cdot e^{wj} - x}}{\left(wj + 1\right) \cdot e^{wj}} \leadsto wj - \frac{\color{blue}{1 \cdot \left(wj \cdot e^{wj} - x\right)}}{\left(wj + 1\right) \cdot e^{wj}}\]
    28.4
  5. Applied times-frac to get
    \[wj - \color{red}{\frac{1 \cdot \left(wj \cdot e^{wj} - x\right)}{\left(wj + 1\right) \cdot e^{wj}}} \leadsto wj - \color{blue}{\frac{1}{wj + 1} \cdot \frac{wj \cdot e^{wj} - x}{e^{wj}}}\]
    28.4
  6. Applied simplify to get
    \[wj - \frac{1}{wj + 1} \cdot \color{red}{\frac{wj \cdot e^{wj} - x}{e^{wj}}} \leadsto wj - \frac{1}{wj + 1} \cdot \color{blue}{\left(wj - \frac{x}{e^{wj}}\right)}\]
    28.3
  7. Applied taylor to get
    \[wj - \frac{1}{wj + 1} \cdot \left(wj - \frac{x}{e^{wj}}\right) \leadsto \left({wj}^2 + x\right) - 2 \cdot \left(wj \cdot x\right)\]
    0.0
  8. Taylor expanded around 0 to get
    \[\color{red}{\left({wj}^2 + x\right) - 2 \cdot \left(wj \cdot x\right)} \leadsto \color{blue}{\left({wj}^2 + x\right) - 2 \cdot \left(wj \cdot x\right)}\]
    0.0
  9. Applied simplify to get
    \[\color{red}{\left({wj}^2 + x\right) - 2 \cdot \left(wj \cdot x\right)} \leadsto \color{blue}{(\left(wj - 2 \cdot x\right) * wj + x)_*}\]
    0.0

Original test:


(lambda ((wj default) (x default))
  #:name "Jmat.Real.lambertw, newton loop step"
  (- wj (/ (- (* wj (exp wj)) x) (+ (exp wj) (* wj (exp wj)))))
  #:target
  (- wj (- (/ wj (+ wj 1)) (/ x (+ (exp wj) (* wj (exp wj)))))))