Average Error: 37.2 → 15.5
Time: 1.1m
Precision: 64
\[\tan \left(x + \varepsilon\right) - \tan x\]
\[\begin{array}{l} \mathbf{if}\;\varepsilon \le -3.0971498034386314 \cdot 10^{-22}:\\ \;\;\;\;(\left(\frac{\tan \varepsilon + \tan x}{1 - \left(\tan x \cdot \tan x\right) \cdot \left(\tan \varepsilon \cdot \tan \varepsilon\right)}\right) \cdot \left(\tan x \cdot \tan \varepsilon + 1\right) + \left(-\tan x\right))_*\\ \mathbf{elif}\;\varepsilon \le 3.432974870891229 \cdot 10^{-42}:\\ \;\;\;\;(\left(x \cdot \varepsilon\right) \cdot \left(x + \varepsilon\right) + \varepsilon)_*\\ \mathbf{else}:\\ \;\;\;\;(\left(\frac{\tan \varepsilon + \tan x}{1 - \left(\tan x \cdot \tan x\right) \cdot \left(\tan \varepsilon \cdot \tan \varepsilon\right)}\right) \cdot \left(\tan x \cdot \tan \varepsilon + 1\right) + \left(-\tan x\right))_*\\ \end{array}\]

Error

Bits error versus x

Bits error versus eps

Target

Original37.2
Target15.0
Herbie15.5
\[\frac{\sin \varepsilon}{\cos x \cdot \cos \left(x + \varepsilon\right)}\]

Derivation

  1. Split input into 2 regimes
  2. if eps < -3.0971498034386314e-22 or 3.432974870891229e-42 < eps

    1. Initial program 30.0

      \[\tan \left(x + \varepsilon\right) - \tan x\]
    2. Using strategy rm
    3. Applied tan-sum2.3

      \[\leadsto \color{blue}{\frac{\tan x + \tan \varepsilon}{1 - \tan x \cdot \tan \varepsilon}} - \tan x\]
    4. Using strategy rm
    5. Applied flip--2.4

      \[\leadsto \frac{\tan x + \tan \varepsilon}{\color{blue}{\frac{1 \cdot 1 - \left(\tan x \cdot \tan \varepsilon\right) \cdot \left(\tan x \cdot \tan \varepsilon\right)}{1 + \tan x \cdot \tan \varepsilon}}} - \tan x\]
    6. Applied associate-/r/2.4

      \[\leadsto \color{blue}{\frac{\tan x + \tan \varepsilon}{1 \cdot 1 - \left(\tan x \cdot \tan \varepsilon\right) \cdot \left(\tan x \cdot \tan \varepsilon\right)} \cdot \left(1 + \tan x \cdot \tan \varepsilon\right)} - \tan x\]
    7. Applied fma-neg2.4

      \[\leadsto \color{blue}{(\left(\frac{\tan x + \tan \varepsilon}{1 \cdot 1 - \left(\tan x \cdot \tan \varepsilon\right) \cdot \left(\tan x \cdot \tan \varepsilon\right)}\right) \cdot \left(1 + \tan x \cdot \tan \varepsilon\right) + \left(-\tan x\right))_*}\]
    8. Using strategy rm
    9. Applied swap-sqr2.4

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

    if -3.0971498034386314e-22 < eps < 3.432974870891229e-42

    1. Initial program 45.9

      \[\tan \left(x + \varepsilon\right) - \tan x\]
    2. Using strategy rm
    3. Applied tan-sum45.9

      \[\leadsto \color{blue}{\frac{\tan x + \tan \varepsilon}{1 - \tan x \cdot \tan \varepsilon}} - \tan x\]
    4. Taylor expanded around 0 31.3

      \[\leadsto \color{blue}{x \cdot {\varepsilon}^{2} + \left(\varepsilon + {x}^{2} \cdot \varepsilon\right)}\]
    5. Simplified31.2

      \[\leadsto \color{blue}{(\left(x \cdot \varepsilon\right) \cdot \left(\varepsilon + x\right) + \varepsilon)_*}\]
  3. Recombined 2 regimes into one program.
  4. Final simplification15.5

    \[\leadsto \begin{array}{l} \mathbf{if}\;\varepsilon \le -3.0971498034386314 \cdot 10^{-22}:\\ \;\;\;\;(\left(\frac{\tan \varepsilon + \tan x}{1 - \left(\tan x \cdot \tan x\right) \cdot \left(\tan \varepsilon \cdot \tan \varepsilon\right)}\right) \cdot \left(\tan x \cdot \tan \varepsilon + 1\right) + \left(-\tan x\right))_*\\ \mathbf{elif}\;\varepsilon \le 3.432974870891229 \cdot 10^{-42}:\\ \;\;\;\;(\left(x \cdot \varepsilon\right) \cdot \left(x + \varepsilon\right) + \varepsilon)_*\\ \mathbf{else}:\\ \;\;\;\;(\left(\frac{\tan \varepsilon + \tan x}{1 - \left(\tan x \cdot \tan x\right) \cdot \left(\tan \varepsilon \cdot \tan \varepsilon\right)}\right) \cdot \left(\tan x \cdot \tan \varepsilon + 1\right) + \left(-\tan x\right))_*\\ \end{array}\]

Reproduce

herbie shell --seed 2019100 +o rules:numerics
(FPCore (x eps)
  :name "2tan (problem 3.3.2)"

  :herbie-target
  (/ (sin eps) (* (cos x) (cos (+ x eps))))

  (- (tan (+ x eps)) (tan x)))