Average Error: 1.1 → 1.2
Time: 27.3s
Precision: 64
Internal Precision: 320
\[\frac{1}{\sqrt{x}} - \frac{1}{\sqrt{x + 1}}\]
\[\frac{\left(\frac{1}{\sqrt{x}} + \frac{1}{\sqrt{x + 1}}\right) \cdot \left(\frac{1}{\sqrt{x}} - \frac{1}{\sqrt{x + 1}}\right)}{\frac{1}{\sqrt{x}} + \frac{1}{\sqrt{x + 1}}}\]

Error

Bits error versus x

Derivation

  1. Initial program 1.1

    \[\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{x}\right)}\right) - \left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{\left(\frac{x}{\left(real->posit(1)\right)}\right)}\right)}\right)\]
  2. Using strategy rm
  3. Applied p16-flip--1.3

    \[\leadsto \color{blue}{\frac{\left(\left(\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{x}\right)}\right) \cdot \left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{x}\right)}\right)\right) - \left(\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{\left(\frac{x}{\left(real->posit(1)\right)}\right)}\right)}\right) \cdot \left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{\left(\frac{x}{\left(real->posit(1)\right)}\right)}\right)}\right)\right)\right)}{\left(\frac{\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{x}\right)}\right)}{\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{\left(\frac{x}{\left(real->posit(1)\right)}\right)}\right)}\right)}\right)}}\]
  4. Using strategy rm
  5. Applied *-commutative1.3

    \[\leadsto \frac{\left(\color{blue}{\left(\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{x}\right)}\right) \cdot \left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{x}\right)}\right)\right)} - \left(\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{\left(\frac{x}{\left(real->posit(1)\right)}\right)}\right)}\right) \cdot \left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{\left(\frac{x}{\left(real->posit(1)\right)}\right)}\right)}\right)\right)\right)}{\left(\frac{\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{x}\right)}\right)}{\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{\left(\frac{x}{\left(real->posit(1)\right)}\right)}\right)}\right)}\right)}\]
  6. Applied difference-of-squares1.2

    \[\leadsto \frac{\color{blue}{\left(\left(\frac{\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{x}\right)}\right)}{\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{\left(\frac{x}{\left(real->posit(1)\right)}\right)}\right)}\right)}\right) \cdot \left(\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{x}\right)}\right) - \left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{\left(\frac{x}{\left(real->posit(1)\right)}\right)}\right)}\right)\right)\right)}}{\left(\frac{\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{x}\right)}\right)}{\left(\frac{\left(real->posit(1)\right)}{\left(\sqrt{\left(\frac{x}{\left(real->posit(1)\right)}\right)}\right)}\right)}\right)}\]
  7. Final simplification1.2

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

Reproduce

herbie shell --seed 2019072 
(FPCore (x)
  :name "2isqrt (example 3.6)"
  (-.p16 (/.p16 (real->posit16 1) (sqrt.p16 x)) (/.p16 (real->posit16 1) (sqrt.p16 (+.p16 x (real->posit16 1))))))