Average Error: 19.5 → 0.4
Time: 7.1s
Precision: binary64
\[\frac{1}{\sqrt{x}} - \frac{1}{\sqrt{x + 1}}\]
↓
\[\frac{\frac{-1}{x}}{\frac{-1 - x}{\sqrt{x}} - \sqrt{x + 1}}\]
\frac{1}{\sqrt{x}} - \frac{1}{\sqrt{x + 1}}
↓
\frac{\frac{-1}{x}}{\frac{-1 - x}{\sqrt{x}} - \sqrt{x + 1}}
(FPCore (x) :precision binary64 (- (/ 1.0 (sqrt x)) (/ 1.0 (sqrt (+ x 1.0)))))
↓
(FPCore (x)
 :precision binary64
 (/ (/ -1.0 x) (- (/ (- -1.0 x) (sqrt x)) (sqrt (+ x 1.0)))))
double code(double x) {
	return (1.0 / sqrt(x)) - (1.0 / sqrt(x + 1.0));
}
↓
double code(double x) {
	return (-1.0 / x) / (((-1.0 - x) / sqrt(x)) - sqrt(x + 1.0));
}

Error

Bits error versus x

Try it out

Your Program's Arguments

Results

Enter valid numbers for all inputs

Target

Original19.5
Target0.6
Herbie0.4
\[\frac{1}{\left(x + 1\right) \cdot \sqrt{x} + x \cdot \sqrt{x + 1}}\]

Derivation

  1. Initial program 19.5

    \[\frac{1}{\sqrt{x}} - \frac{1}{\sqrt{x + 1}}\]
  2. Using strategy rm

  3. Applied flip--_binary64_211819.6

    \[\leadsto \color{blue}{\frac{\frac{1}{\sqrt{x}} \cdot \frac{1}{\sqrt{x}} - \frac{1}{\sqrt{x + 1}} \cdot \frac{1}{\sqrt{x + 1}}}{\frac{1}{\sqrt{x}} + \frac{1}{\sqrt{x + 1}}}}\]

  4. Simplified19.6

    \[\leadsto \frac{\color{blue}{\frac{1}{x} - \frac{1}{1 + x}}}{\frac{1}{\sqrt{x}} + \frac{1}{\sqrt{x + 1}}}\]

  5. Simplified19.6

    \[\leadsto \frac{\frac{1}{x} - \frac{1}{1 + x}}{\color{blue}{\frac{1}{\sqrt{x}} + \frac{1}{\sqrt{1 + x}}}}\]
  6. Using strategy rm

  7. Applied frac-sub_binary64_215219.0

    \[\leadsto \frac{\color{blue}{\frac{1 \cdot \left(1 + x\right) - x \cdot 1}{x \cdot \left(1 + x\right)}}}{\frac{1}{\sqrt{x}} + \frac{1}{\sqrt{1 + x}}}\]

  8. Simplified5.9

    \[\leadsto \frac{\frac{\color{blue}{1}}{x \cdot \left(1 + x\right)}}{\frac{1}{\sqrt{x}} + \frac{1}{\sqrt{1 + x}}}\]
  9. Using strategy rm

  10. Applied add-sqr-sqrt_binary64_21655.9

    \[\leadsto \frac{\frac{\color{blue}{\sqrt{1} \cdot \sqrt{1}}}{x \cdot \left(1 + x\right)}}{\frac{1}{\sqrt{x}} + \frac{1}{\sqrt{1 + x}}}\]

  11. Applied times-frac_binary64_21495.4

    \[\leadsto \frac{\color{blue}{\frac{\sqrt{1}}{x} \cdot \frac{\sqrt{1}}{1 + x}}}{\frac{1}{\sqrt{x}} + \frac{1}{\sqrt{1 + x}}}\]

  12. Applied associate-/l*_binary64_20880.4

    \[\leadsto \color{blue}{\frac{\frac{\sqrt{1}}{x}}{\frac{\frac{1}{\sqrt{x}} + \frac{1}{\sqrt{1 + x}}}{\frac{\sqrt{1}}{1 + x}}}}\]

  13. Simplified0.4

    \[\leadsto \frac{\frac{\sqrt{1}}{x}}{\color{blue}{\left(x + 1\right) \cdot \left(\frac{1}{\sqrt{x}} + \frac{1}{\sqrt{x + 1}}\right)}}\]
  14. Using strategy rm

  15. Applied frac-2neg_binary64_21540.4

    \[\leadsto \color{blue}{\frac{-\frac{\sqrt{1}}{x}}{-\left(x + 1\right) \cdot \left(\frac{1}{\sqrt{x}} + \frac{1}{\sqrt{x + 1}}\right)}}\]

  16. Simplified0.4

    \[\leadsto \frac{\color{blue}{\frac{-1}{x}}}{-\left(x + 1\right) \cdot \left(\frac{1}{\sqrt{x}} + \frac{1}{\sqrt{x + 1}}\right)}\]

  17. Simplified0.4

    \[\leadsto \frac{\frac{-1}{x}}{\color{blue}{\frac{-1 - x}{\sqrt{x}} - \sqrt{1 + x}}}\]

  18. Final simplification0.4

    \[\leadsto \frac{\frac{-1}{x}}{\frac{-1 - x}{\sqrt{x}} - \sqrt{x + 1}}\]

Reproduce

herbie shell --seed 2020280 
(FPCore (x)
  :name "2isqrt (example 3.6)"
  :precision binary64

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

  (- (/ 1.0 (sqrt x)) (/ 1.0 (sqrt (+ x 1.0)))))