2atan (example 3.5)

Average Error: 14.5 → 0.3

Time: 3.9s

Precision: binary64

Math

\[\tan^{-1} \left(N + 1\right) - \tan^{-1} N \]

↓

\[\tan^{-1}_* \frac{1 + \left(N - N\right)}{1 + N \cdot \left(1 + N\right)} \]

FPCore

(FPCore (N) :precision binary64 (- (atan (+ N 1.0)) (atan N)))

↓

(FPCore (N)
 :precision binary64
 (atan2 (+ 1.0 (- N N)) (+ 1.0 (* N (+ 1.0 N)))))

C

double code(double N) {
	return atan((N + 1.0)) - atan(N);
}

↓

double code(double N) {
	return atan2((1.0 + (N - N)), (1.0 + (N * (1.0 + N))));
}

Fortran

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

↓

real(8) function code(n)
    real(8), intent (in) :: n
    code = atan2((1.0d0 + (n - n)), (1.0d0 + (n * (1.0d0 + n))))
end function

Java

public static double code(double N) {
	return Math.atan((N + 1.0)) - Math.atan(N);
}

↓

public static double code(double N) {
	return Math.atan2((1.0 + (N - N)), (1.0 + (N * (1.0 + N))));
}

Python

def code(N):
	return math.atan((N + 1.0)) - math.atan(N)

↓

def code(N):
	return math.atan2((1.0 + (N - N)), (1.0 + (N * (1.0 + N))))

Julia

function code(N)
	return Float64(atan(Float64(N + 1.0)) - atan(N))
end

↓

function code(N)
	return atan(Float64(1.0 + Float64(N - N)), Float64(1.0 + Float64(N * Float64(1.0 + N))))
end

MATLAB

function tmp = code(N)
	tmp = atan((N + 1.0)) - atan(N);
end

↓

function tmp = code(N)
	tmp = atan2((1.0 + (N - N)), (1.0 + (N * (1.0 + N))));
end

Wolfram

code[N_] := N[(N[ArcTan[N[(N + 1.0), $MachinePrecision]], $MachinePrecision] - N[ArcTan[N], $MachinePrecision]), $MachinePrecision]

↓

code[N_] := N[ArcTan[N[(1.0 + N[(N - N), $MachinePrecision]), $MachinePrecision] / N[(1.0 + N[(N * N[(1.0 + N), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]], $MachinePrecision]

Target

Original	14.5
Target	0.3
Herbie	0.3

\[\tan^{-1} \left(\frac{1}{1 + N \cdot \left(N + 1\right)}\right) \]

Derivation

1. Initial program 14.5

   \[\tan^{-1} \left(N + 1\right) - \tan^{-1} N \]

2. Applied egg-rr 0.3

   \[\leadsto \color{blue}{\tan^{-1}_* \frac{1 + \left(N - N\right)}{1 + N \cdot \left(N + 1\right)}} \]

3. Final simplification 0.3

   \[\leadsto \tan^{-1}_* \frac{1 + \left(N - N\right)}{1 + N \cdot \left(1 + N\right)} \]

Reproduce

herbie shell --seed 2022210 
(FPCore (N)
  :name "2atan (example 3.5)"
  :precision binary64

  :herbie-target
  (atan (/ 1.0 (+ 1.0 (* N (+ N 1.0)))))

  (- (atan (+ N 1.0)) (atan N)))