Average Error: 61.2 → 2.1
Time: 16.1s
Precision: binary64
\[-\frac{1}{\frac{\pi}{4}} \cdot \log \left(\frac{e^{\frac{\pi}{4} \cdot f} + e^{-\frac{\pi}{4} \cdot f}}{e^{\frac{\pi}{4} \cdot f} - e^{-\frac{\pi}{4} \cdot f}}\right)\]
\[\sqrt{\frac{1}{\frac{\pi}{4}}} \cdot \left(\log \left(\frac{\cosh \left(\pi \cdot \frac{f}{4}\right)}{\sinh \left(\pi \cdot \frac{f}{4}\right)}\right) \cdot \left(-\sqrt{4 \cdot \frac{1}{\pi}}\right)\right)\]

Error

Bits error versus f

Derivation

  1. Initial program 61.2

    \[-\frac{1}{\frac{\pi}{4}} \cdot \log \left(\frac{e^{\frac{\pi}{4} \cdot f} + e^{-\frac{\pi}{4} \cdot f}}{e^{\frac{\pi}{4} \cdot f} - e^{-\frac{\pi}{4} \cdot f}}\right)\]
  2. Using strategy rm
  3. Applied sinh-undef2.1

    \[\leadsto -\frac{1}{\frac{\pi}{4}} \cdot \log \left(\frac{e^{\frac{\pi}{4} \cdot f} + e^{-\frac{\pi}{4} \cdot f}}{\color{blue}{2 \cdot \sinh \left(\frac{\pi}{4} \cdot f\right)}}\right)\]
  4. Applied associate-/r*2.1

    \[\leadsto -\frac{1}{\frac{\pi}{4}} \cdot \log \color{blue}{\left(\frac{\frac{e^{\frac{\pi}{4} \cdot f} + e^{-\frac{\pi}{4} \cdot f}}{2}}{\sinh \left(\frac{\pi}{4} \cdot f\right)}\right)}\]
  5. Simplified2.1

    \[\leadsto -\frac{1}{\frac{\pi}{4}} \cdot \log \left(\frac{\color{blue}{\cosh \left(\pi \cdot \frac{f}{4}\right)}}{\sinh \left(\frac{\pi}{4} \cdot f\right)}\right)\]
  6. Using strategy rm
  7. Applied add-sqr-sqrt2.4

    \[\leadsto -\color{blue}{\left(\sqrt{\frac{1}{\frac{\pi}{4}}} \cdot \sqrt{\frac{1}{\frac{\pi}{4}}}\right)} \cdot \log \left(\frac{\cosh \left(\pi \cdot \frac{f}{4}\right)}{\sinh \left(\frac{\pi}{4} \cdot f\right)}\right)\]
  8. Applied associate-*l*2.1

    \[\leadsto -\color{blue}{\sqrt{\frac{1}{\frac{\pi}{4}}} \cdot \left(\sqrt{\frac{1}{\frac{\pi}{4}}} \cdot \log \left(\frac{\cosh \left(\pi \cdot \frac{f}{4}\right)}{\sinh \left(\frac{\pi}{4} \cdot f\right)}\right)\right)}\]
  9. Simplified2.1

    \[\leadsto -\sqrt{\frac{1}{\frac{\pi}{4}}} \cdot \color{blue}{\left(\log \left(\frac{\cosh \left(\pi \cdot \frac{f}{4}\right)}{\sinh \left(\pi \cdot \frac{f}{4}\right)}\right) \cdot \sqrt{4 \cdot \frac{1}{\pi}}\right)}\]
  10. Final simplification2.1

    \[\leadsto \sqrt{\frac{1}{\frac{\pi}{4}}} \cdot \left(\log \left(\frac{\cosh \left(\pi \cdot \frac{f}{4}\right)}{\sinh \left(\pi \cdot \frac{f}{4}\right)}\right) \cdot \left(-\sqrt{4 \cdot \frac{1}{\pi}}\right)\right)\]

Reproduce

herbie shell --seed 2020185 
(FPCore (f)
  :name "VandenBroeck and Keller, Equation (20)"
  :precision binary64
  (neg (* (/ 1.0 (/ PI 4.0)) (log (/ (+ (exp (* (/ PI 4.0) f)) (exp (neg (* (/ PI 4.0) f)))) (- (exp (* (/ PI 4.0) f)) (exp (neg (* (/ PI 4.0) f)))))))))