Average Error: 58.6 → 0.2
Time: 24.5s
Precision: 64
Internal Precision: 128
\[\log \left(\frac{1 - \varepsilon}{1 + \varepsilon}\right)\]
\[\left({\varepsilon}^{5} \cdot \frac{-2}{5} - 2 \cdot \varepsilon\right) - \left(\varepsilon \cdot \varepsilon\right) \cdot \left(\frac{2}{3} \cdot \varepsilon\right)\]

Error

Bits error versus eps

Target

Original58.6
Target0.2
Herbie0.2
\[-2 \cdot \left(\left(\varepsilon + \frac{{\varepsilon}^{3}}{3}\right) + \frac{{\varepsilon}^{5}}{5}\right)\]

Derivation

  1. Initial program 58.6

    \[\log \left(\frac{1 - \varepsilon}{1 + \varepsilon}\right)\]
  2. Taylor expanded around 0 0.2

    \[\leadsto \color{blue}{-\left(\frac{2}{3} \cdot {\varepsilon}^{3} + \left(\frac{2}{5} \cdot {\varepsilon}^{5} + 2 \cdot \varepsilon\right)\right)}\]
  3. Simplified0.2

    \[\leadsto \color{blue}{{\varepsilon}^{5} \cdot \frac{-2}{5} - \varepsilon \cdot \left(2 - \varepsilon \cdot \left(\varepsilon \cdot \frac{-2}{3}\right)\right)}\]
  4. Using strategy rm
  5. Applied sub-neg0.2

    \[\leadsto {\varepsilon}^{5} \cdot \frac{-2}{5} - \varepsilon \cdot \color{blue}{\left(2 + \left(-\varepsilon \cdot \left(\varepsilon \cdot \frac{-2}{3}\right)\right)\right)}\]
  6. Applied distribute-rgt-in0.2

    \[\leadsto {\varepsilon}^{5} \cdot \frac{-2}{5} - \color{blue}{\left(2 \cdot \varepsilon + \left(-\varepsilon \cdot \left(\varepsilon \cdot \frac{-2}{3}\right)\right) \cdot \varepsilon\right)}\]
  7. Applied associate--r+0.2

    \[\leadsto \color{blue}{\left({\varepsilon}^{5} \cdot \frac{-2}{5} - 2 \cdot \varepsilon\right) - \left(-\varepsilon \cdot \left(\varepsilon \cdot \frac{-2}{3}\right)\right) \cdot \varepsilon}\]
  8. Simplified0.2

    \[\leadsto \left({\varepsilon}^{5} \cdot \frac{-2}{5} - 2 \cdot \varepsilon\right) - \color{blue}{\left(\varepsilon \cdot \varepsilon\right) \cdot \left(\varepsilon \cdot \frac{2}{3}\right)}\]
  9. Final simplification0.2

    \[\leadsto \left({\varepsilon}^{5} \cdot \frac{-2}{5} - 2 \cdot \varepsilon\right) - \left(\varepsilon \cdot \varepsilon\right) \cdot \left(\frac{2}{3} \cdot \varepsilon\right)\]

Reproduce

herbie shell --seed 2019050 
(FPCore (eps)
  :name "logq (problem 3.4.3)"

  :herbie-target
  (* -2 (+ (+ eps (/ (pow eps 3) 3)) (/ (pow eps 5) 5)))

  (log (/ (- 1 eps) (+ 1 eps))))