cos2 (problem 3.4.1)

Average Error: 31.6 → 0.1

Time: 11.2s

Precision: binary64

Cost: 13504

Math

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

↓

\[-\frac{\tan \left(x \cdot 0.5\right) \cdot \frac{\sin x}{x}}{-x} \]

FPCore

(FPCore (x) :precision binary64 (/ (- 1.0 (cos x)) (* x x)))

↓

(FPCore (x)
 :precision binary64
 (- (/ (* (tan (* x 0.5)) (/ (sin x) x)) (- x))))

C

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

↓

double code(double x) {
	return -((tan((x * 0.5)) * (sin(x) / x)) / -x);
}

Fortran

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

↓

real(8) function code(x)
    real(8), intent (in) :: x
    code = -((tan((x * 0.5d0)) * (sin(x) / x)) / -x)
end function

Java

public static double code(double x) {
	return (1.0 - Math.cos(x)) / (x * x);
}

↓

public static double code(double x) {
	return -((Math.tan((x * 0.5)) * (Math.sin(x) / x)) / -x);
}

Python

def code(x):
	return (1.0 - math.cos(x)) / (x * x)

↓

def code(x):
	return -((math.tan((x * 0.5)) * (math.sin(x) / x)) / -x)

Julia

function code(x)
	return Float64(Float64(1.0 - cos(x)) / Float64(x * x))
end

↓

function code(x)
	return Float64(-Float64(Float64(tan(Float64(x * 0.5)) * Float64(sin(x) / x)) / Float64(-x)))
end

MATLAB

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

↓

function tmp = code(x)
	tmp = -((tan((x * 0.5)) * (sin(x) / x)) / -x);
end

Wolfram

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

↓

code[x_] := (-N[(N[(N[Tan[N[(x * 0.5), $MachinePrecision]], $MachinePrecision] * N[(N[Sin[x], $MachinePrecision] / x), $MachinePrecision]), $MachinePrecision] / (-x)), $MachinePrecision])

Derivation

1. Initial program 31.6

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

2. Applied egg-rr 15.9

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

3. Simplified 15.8

   \[\leadsto \frac{\color{blue}{\sin x \cdot \tan \left(\frac{x}{2}\right)}}{x \cdot x} \]
   Proof

   [Start] 15.9	\[ \frac{\left(\sin x \cdot \sin x\right) \cdot \frac{1}{1 + \cos x}}{x \cdot x} \]
   associate-*l* [=>] 15.9	\[ \frac{\color{blue}{\sin x \cdot \left(\sin x \cdot \frac{1}{1 + \cos x}\right)}}{x \cdot x} \]
   associate-*r/ [=>] 15.9	\[ \frac{\sin x \cdot \color{blue}{\frac{\sin x \cdot 1}{1 + \cos x}}}{x \cdot x} \]
   *-rgt-identity [=>] 15.9	\[ \frac{\sin x \cdot \frac{\color{blue}{\sin x}}{1 + \cos x}}{x \cdot x} \]
   hang-0p-tan [=>] 15.8	\[ \frac{\sin x \cdot \color{blue}{\tan \left(\frac{x}{2}\right)}}{x \cdot x} \]

4. Applied egg-rr 0.1

   \[\leadsto \color{blue}{-\frac{\tan \left(x \cdot 0.5\right) \cdot \frac{\sin x}{x}}{-x}} \]

5. Final simplification 0.1

   \[\leadsto -\frac{\tan \left(x \cdot 0.5\right) \cdot \frac{\sin x}{x}}{-x} \]

Alternatives

Alternative 1
Error	0.3
Cost	13640

\[\begin{array}{l} \mathbf{if}\;x \leq -0.0032:\\ \;\;\;\;\frac{\frac{1 - \cos x}{x}}{x}\\ \mathbf{elif}\;x \leq 10^{-7}:\\ \;\;\;\;0.5 + -0.041666666666666664 \cdot \left(x \cdot x\right)\\ \mathbf{else}:\\ \;\;\;\;\frac{\sin x}{x \cdot x} \cdot \tan \left(\frac{x}{2}\right)\\ \end{array} \]

Alternative 2
Error	0.1
Cost	13376

\[\frac{\sin x}{x} \cdot \frac{\tan \left(x \cdot 0.5\right)}{x} \]

Alternative 3
Error	0.5
Cost	7113

\[\begin{array}{l} \mathbf{if}\;x \leq -0.0032 \lor \neg \left(x \leq 0.0046\right):\\ \;\;\;\;\frac{1 - \cos x}{x \cdot x}\\ \mathbf{else}:\\ \;\;\;\;0.5 + -0.041666666666666664 \cdot \left(x \cdot x\right)\\ \end{array} \]

Alternative 4
Error	0.3
Cost	7113

\[\begin{array}{l} \mathbf{if}\;x \leq -0.0032 \lor \neg \left(x \leq 0.0046\right):\\ \;\;\;\;\frac{\frac{1 - \cos x}{x}}{x}\\ \mathbf{else}:\\ \;\;\;\;0.5 + -0.041666666666666664 \cdot \left(x \cdot x\right)\\ \end{array} \]

Alternative 5
Error	15.4
Cost	969

\[\begin{array}{l} \mathbf{if}\;x \leq -8 \cdot 10^{+68} \lor \neg \left(x \leq 1.25 \cdot 10^{+77}\right):\\ \;\;\;\;\frac{\frac{1}{x}}{x} + \frac{-1}{x \cdot x}\\ \mathbf{else}:\\ \;\;\;\;0.5\\ \end{array} \]

Alternative 6
Error	30.8
Cost	64

\[0.5 \]

Reproduce

herbie shell --seed 2023017 
(FPCore (x)
  :name "cos2 (problem 3.4.1)"
  :precision binary64
  (/ (- 1.0 (cos x)) (* x x)))