Rust f64::acosh

Percentage Accurate: 50.4% → 99.5%

Time: 2.0s

Alternatives: 2

Speedup: N/A×

Specification

\[\log \left(x + \sqrt{x \cdot x - 1}\right) \]

In
Out

Enter valid numbers for all inputs

Local Percentage Accuracy vs ?

The average percentage accuracy by input value. Horizontal axis shows value of an input variable; the variable is choosen in the title. Vertical axis is accuracy; higher is better. Red represent the original program, while blue represents Herbie's suggestion. These can be toggled with buttons below the plot. The line is an average while dots represent individual samples.

Accuracy vs Speed?

Herbie found 2 alternatives:

Alternative	Accuracy	Speedup

The accuracy (vertical axis) and speed (horizontal axis) of each alternatives. Up and to the right is better. The red square shows the initial program, and each blue circle shows an alternative.The line shows the best available speed-accuracy tradeoffs.

Alternative 1: 99.5% accurate, 1.9× speedup?

\[\log \left(x \cdot 2 - \frac{0.5}{x}\right) \]

Derivation

Initial program 53.8%
\[\log \left(x + \sqrt{x \cdot x - 1}\right) \]
Taylor expanded in x around inf 99.7%
\[\leadsto \log \color{blue}{\left(2 \cdot x - 0.5 \cdot \frac{1}{x}\right)} \]
Step-by-step derivation
1. *-commutative99.7%
  \[\leadsto \log \left(\color{blue}{x \cdot 2} - 0.5 \cdot \frac{1}{x}\right) \]
2. associate-*r/99.7%
  \[\leadsto \log \left(x \cdot 2 - \color{blue}{\frac{0.5 \cdot 1}{x}}\right) \]
3. metadata-eval99.7%
  \[\leadsto \log \left(x \cdot 2 - \frac{\color{blue}{0.5}}{x}\right) \]
Simplified99.7%
\[\leadsto \log \color{blue}{\left(x \cdot 2 - \frac{0.5}{x}\right)} \]
Final simplification99.7%
\[\leadsto \log \left(x \cdot 2 - \frac{0.5}{x}\right) \]

Alternative 2: 99.1% accurate, 2.0× speedup?

\[\log \left(x + x\right) \]

Derivation

Initial program 53.8%
\[\log \left(x + \sqrt{x \cdot x - 1}\right) \]
Taylor expanded in x around inf 99.3%
\[\leadsto \log \left(x + \color{blue}{x}\right) \]
Final simplification99.3%
\[\leadsto \log \left(x + x\right) \]

Developer target: 99.9% accurate, 0.7× speedup?

\[\log \left(x + \sqrt{x - 1} \cdot \sqrt{x + 1}\right) \]

Reproduce

herbie shell --seed 2023167 
(FPCore (x)
  :name "Rust f64::acosh"
  :precision binary64
  :pre (>= x 1.0)

  :herbie-target
  (log (+ x (* (sqrt (- x 1.0)) (sqrt (+ x 1.0)))))

  (log (+ x (sqrt (- (* x x) 1.0)))))