sqrt B (should all be same)

Percentage Accurate: 53.6% → 99.4%
Time: 2.3s
Alternatives: 3
Speedup: 1.0×

Specification

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\[\sqrt{\left(2 \cdot x\right) \cdot x} \]

Your Program's Arguments

Results

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 3 alternatives:

AlternativeAccuracySpeedup
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: 99.4% accurate, 0.5× speedup?

\[\begin{array}{l} \mathbf{if}\;x \leq -2 \cdot 10^{-310}:\\ \;\;\;\;x \cdot \left(-\sqrt{2}\right)\\ \mathbf{else}:\\ \;\;\;\;\sqrt{x \cdot 2} \cdot \sqrt{x}\\ \end{array} \]
Derivation
  1. Split input into 2 regimes

  2. if x < -1.999999999999994e-310

    1. Initial program 52.8%

      \[\sqrt{\left(2 \cdot x\right) \cdot x} \]

    2. Taylor expanded in x around -inf 99.4%

      \[\leadsto \color{blue}{-1 \cdot \left(\sqrt{2} \cdot x\right)} \]
    3. Step-by-step derivation

      1. mul-1-neg99.4%

        \[\leadsto \color{blue}{-\sqrt{2} \cdot x} \]

      2. distribute-rgt-neg-in99.4%

        \[\leadsto \color{blue}{\sqrt{2} \cdot \left(-x\right)} \]

    4. Simplified99.4%

      \[\leadsto \color{blue}{\sqrt{2} \cdot \left(-x\right)} \]

    if -1.999999999999994e-310 < x

    1. Initial program 58.7%

      \[\sqrt{\left(2 \cdot x\right) \cdot x} \]
    2. Step-by-step derivation

      1. sqrt-prod99.5%

        \[\leadsto \color{blue}{\sqrt{2 \cdot x} \cdot \sqrt{x}} \]

    3. Applied egg-rr99.5%

      \[\leadsto \color{blue}{\sqrt{2 \cdot x} \cdot \sqrt{x}} \]
  3. Recombined 2 regimes into one program.

  4. Final simplification99.4%

    \[\leadsto \begin{array}{l} \mathbf{if}\;x \leq -2 \cdot 10^{-310}:\\ \;\;\;\;x \cdot \left(-\sqrt{2}\right)\\ \mathbf{else}:\\ \;\;\;\;\sqrt{x \cdot 2} \cdot \sqrt{x}\\ \end{array} \]

Alternative 2: 99.3% accurate, 1.0× speedup?

\[\begin{array}{l} \mathbf{if}\;x \leq -2 \cdot 10^{-310}:\\ \;\;\;\;x \cdot \left(-\sqrt{2}\right)\\ \mathbf{else}:\\ \;\;\;\;x \cdot \sqrt{2}\\ \end{array} \]
Derivation
  1. Split input into 2 regimes

  2. if x < -1.999999999999994e-310

    1. Initial program 52.8%

      \[\sqrt{\left(2 \cdot x\right) \cdot x} \]

    2. Taylor expanded in x around -inf 99.4%

      \[\leadsto \color{blue}{-1 \cdot \left(\sqrt{2} \cdot x\right)} \]
    3. Step-by-step derivation

      1. mul-1-neg99.4%

        \[\leadsto \color{blue}{-\sqrt{2} \cdot x} \]

      2. distribute-rgt-neg-in99.4%

        \[\leadsto \color{blue}{\sqrt{2} \cdot \left(-x\right)} \]

    4. Simplified99.4%

      \[\leadsto \color{blue}{\sqrt{2} \cdot \left(-x\right)} \]

    if -1.999999999999994e-310 < x

    1. Initial program 58.7%

      \[\sqrt{\left(2 \cdot x\right) \cdot x} \]

    2. Taylor expanded in x around 0 99.4%

      \[\leadsto \color{blue}{\sqrt{2} \cdot x} \]
  3. Recombined 2 regimes into one program.

  4. Final simplification99.4%

    \[\leadsto \begin{array}{l} \mathbf{if}\;x \leq -2 \cdot 10^{-310}:\\ \;\;\;\;x \cdot \left(-\sqrt{2}\right)\\ \mathbf{else}:\\ \;\;\;\;x \cdot \sqrt{2}\\ \end{array} \]

Alternative 3: 50.4% accurate, 1.0× speedup?

\[x \cdot \sqrt{2} \]
Derivation

  1. Initial program 55.8%

    \[\sqrt{\left(2 \cdot x\right) \cdot x} \]

  2. Taylor expanded in x around 0 51.1%

    \[\leadsto \color{blue}{\sqrt{2} \cdot x} \]

  3. Final simplification51.1%

    \[\leadsto x \cdot \sqrt{2} \]

Reproduce

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herbie shell --seed 2023167 
(FPCore (x)
  :name "sqrt B (should all be same)"
  :precision binary64
  (sqrt (* (* 2.0 x) x)))