2frac (problem 3.3.1)

Average Accuracy: 78.0% → 99.9%

Time: 5.4s

Precision: binary64

Cost: 448

Math

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

↓

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

FPCore

(FPCore (x) :precision binary64 (- (/ 1.0 (+ x 1.0)) (/ 1.0 x)))

↓

(FPCore (x) :precision binary64 (/ (/ -1.0 x) (+ x 1.0)))

C

double code(double x) {
	return (1.0 / (x + 1.0)) - (1.0 / x);
}

↓

double code(double x) {
	return (-1.0 / x) / (x + 1.0);
}

Fortran

real(8) function code(x)
    real(8), intent (in) :: x
    code = (1.0d0 / (x + 1.0d0)) - (1.0d0 / x)
end function

↓

real(8) function code(x)
    real(8), intent (in) :: x
    code = ((-1.0d0) / x) / (x + 1.0d0)
end function

Java

public static double code(double x) {
	return (1.0 / (x + 1.0)) - (1.0 / x);
}

↓

public static double code(double x) {
	return (-1.0 / x) / (x + 1.0);
}

Python

def code(x):
	return (1.0 / (x + 1.0)) - (1.0 / x)

↓

def code(x):
	return (-1.0 / x) / (x + 1.0)

Julia

function code(x)
	return Float64(Float64(1.0 / Float64(x + 1.0)) - Float64(1.0 / x))
end

↓

function code(x)
	return Float64(Float64(-1.0 / x) / Float64(x + 1.0))
end

MATLAB

function tmp = code(x)
	tmp = (1.0 / (x + 1.0)) - (1.0 / x);
end

↓

function tmp = code(x)
	tmp = (-1.0 / x) / (x + 1.0);
end

Wolfram

code[x_] := N[(N[(1.0 / N[(x + 1.0), $MachinePrecision]), $MachinePrecision] - N[(1.0 / x), $MachinePrecision]), $MachinePrecision]

↓

code[x_] := N[(N[(-1.0 / x), $MachinePrecision] / N[(x + 1.0), $MachinePrecision]), $MachinePrecision]

Derivation

1. Initial program 78.0%

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

2. Applied egg-rr 79.0%

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

   [Start] 78.0	\[ \frac{1}{x + 1} - \frac{1}{x} \]
   frac-sub [=>] 79.0	\[ \color{blue}{\frac{1 \cdot x - \left(x + 1\right) \cdot 1}{\left(x + 1\right) \cdot x}} \]
   *-commutative [=>] 79.0	\[ \frac{1 \cdot x - \left(x + 1\right) \cdot 1}{\color{blue}{x \cdot \left(x + 1\right)}} \]
   associate-/r* [=>] 79.0	\[ \color{blue}{\frac{\frac{1 \cdot x - \left(x + 1\right) \cdot 1}{x}}{x + 1}} \]
   *-un-lft-identity [<=] 79.0	\[ \frac{\frac{\color{blue}{x} - \left(x + 1\right) \cdot 1}{x}}{x + 1} \]
   cancel-sign-sub-inv [=>] 79.0	\[ \frac{\frac{\color{blue}{x + \left(-\left(x + 1\right)\right) \cdot 1}}{x}}{x + 1} \]
   *-commutative [<=] 79.0	\[ \frac{\frac{x + \color{blue}{1 \cdot \left(-\left(x + 1\right)\right)}}{x}}{x + 1} \]
   *-un-lft-identity [<=] 79.0	\[ \frac{\frac{x + \color{blue}{\left(-\left(x + 1\right)\right)}}{x}}{x + 1} \]
   +-commutative [=>] 79.0	\[ \frac{\frac{x + \left(-\color{blue}{\left(1 + x\right)}\right)}{x}}{x + 1} \]
   distribute-neg-in [=>] 79.0	\[ \frac{\frac{x + \color{blue}{\left(\left(-1\right) + \left(-x\right)\right)}}{x}}{x + 1} \]
   neg-sub0 [=>] 79.0	\[ \frac{\frac{x + \left(\left(-1\right) + \color{blue}{\left(0 - x\right)}\right)}{x}}{x + 1} \]
   metadata-eval [<=] 79.0	\[ \frac{\frac{x + \left(\left(-1\right) + \left(\color{blue}{\log 1} - x\right)\right)}{x}}{x + 1} \]
   associate-+r- [=>] 79.0	\[ \frac{\frac{x + \color{blue}{\left(\left(\left(-1\right) + \log 1\right) - x\right)}}{x}}{x + 1} \]
   metadata-eval [=>] 79.0	\[ \frac{\frac{x + \left(\left(\color{blue}{-1} + \log 1\right) - x\right)}{x}}{x + 1} \]
   metadata-eval [=>] 79.0	\[ \frac{\frac{x + \left(\left(-1 + \color{blue}{0}\right) - x\right)}{x}}{x + 1} \]
   metadata-eval [=>] 79.0	\[ \frac{\frac{x + \left(\color{blue}{-1} - x\right)}{x}}{x + 1} \]
   +-commutative [=>] 79.0	\[ \frac{\frac{x + \left(-1 - x\right)}{x}}{\color{blue}{1 + x}} \]

3. Taylor expanded in x around 0 99.9%

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

4. Final simplification 99.9%

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

Alternatives

Alternative 1
Accuracy	98.1%
Cost	713

\[\begin{array}{l} \mathbf{if}\;x \leq -1 \lor \neg \left(x \leq 1\right):\\ \;\;\;\;\frac{-1}{x \cdot x}\\ \mathbf{else}:\\ \;\;\;\;\left(1 - x\right) + \frac{-1}{x}\\ \end{array} \]

Alternative 2
Accuracy	98.0%
Cost	585

\[\begin{array}{l} \mathbf{if}\;x \leq -1 \lor \neg \left(x \leq 0.76\right):\\ \;\;\;\;\frac{-1}{x \cdot x}\\ \mathbf{else}:\\ \;\;\;\;1 + \frac{-1}{x}\\ \end{array} \]

Alternative 3
Accuracy	52.1%
Cost	192

\[\frac{-1}{x} \]

Reproduce

herbie shell --seed 2023137 
(FPCore (x)
  :name "2frac (problem 3.3.1)"
  :precision binary64
  (- (/ 1.0 (+ x 1.0)) (/ 1.0 x)))