Average Error: 13.2 → 0.2
Time: 14.3s
Precision: binary64
Cost: 60868
\[wj - \frac{wj \cdot e^{wj} - x}{e^{wj} + wj \cdot e^{wj}} \]
\[\begin{array}{l} t_0 := \frac{x}{e^{wj} \cdot \left(wj + 1\right)}\\ t_1 := wj \cdot e^{wj}\\ t_2 := \frac{wj}{\mathsf{fma}\left(wj, wj, -1\right)}\\ \mathbf{if}\;wj + \frac{x - t_1}{e^{wj} + t_1} \leq 2 \cdot 10^{-10}:\\ \;\;\;\;\mathsf{fma}\left(wj, wj, \left({wj}^{4} - {wj}^{3}\right) - {wj}^{5}\right) + t_0\\ \mathbf{else}:\\ \;\;\;\;t_0 + \left(\mathsf{fma}\left(wj, 1, t_2 \cdot \left(1 - wj\right)\right) + \mathsf{fma}\left(1 - wj, t_2, \left(wj + -1\right) \cdot t_2\right)\right)\\ \end{array} \]
(FPCore (wj x)
 :precision binary64
 (- wj (/ (- (* wj (exp wj)) x) (+ (exp wj) (* wj (exp wj))))))
(FPCore (wj x)
 :precision binary64
 (let* ((t_0 (/ x (* (exp wj) (+ wj 1.0))))
        (t_1 (* wj (exp wj)))
        (t_2 (/ wj (fma wj wj -1.0))))
   (if (<= (+ wj (/ (- x t_1) (+ (exp wj) t_1))) 2e-10)
     (+ (fma wj wj (- (- (pow wj 4.0) (pow wj 3.0)) (pow wj 5.0))) t_0)
     (+
      t_0
      (+
       (fma wj 1.0 (* t_2 (- 1.0 wj)))
       (fma (- 1.0 wj) t_2 (* (+ wj -1.0) t_2)))))))
double code(double wj, double x) {
	return wj - (((wj * exp(wj)) - x) / (exp(wj) + (wj * exp(wj))));
}
double code(double wj, double x) {
	double t_0 = x / (exp(wj) * (wj + 1.0));
	double t_1 = wj * exp(wj);
	double t_2 = wj / fma(wj, wj, -1.0);
	double tmp;
	if ((wj + ((x - t_1) / (exp(wj) + t_1))) <= 2e-10) {
		tmp = fma(wj, wj, ((pow(wj, 4.0) - pow(wj, 3.0)) - pow(wj, 5.0))) + t_0;
	} else {
		tmp = t_0 + (fma(wj, 1.0, (t_2 * (1.0 - wj))) + fma((1.0 - wj), t_2, ((wj + -1.0) * t_2)));
	}
	return tmp;
}
function code(wj, x)
	return Float64(wj - Float64(Float64(Float64(wj * exp(wj)) - x) / Float64(exp(wj) + Float64(wj * exp(wj)))))
end
function code(wj, x)
	t_0 = Float64(x / Float64(exp(wj) * Float64(wj + 1.0)))
	t_1 = Float64(wj * exp(wj))
	t_2 = Float64(wj / fma(wj, wj, -1.0))
	tmp = 0.0
	if (Float64(wj + Float64(Float64(x - t_1) / Float64(exp(wj) + t_1))) <= 2e-10)
		tmp = Float64(fma(wj, wj, Float64(Float64((wj ^ 4.0) - (wj ^ 3.0)) - (wj ^ 5.0))) + t_0);
	else
		tmp = Float64(t_0 + Float64(fma(wj, 1.0, Float64(t_2 * Float64(1.0 - wj))) + fma(Float64(1.0 - wj), t_2, Float64(Float64(wj + -1.0) * t_2))));
	end
	return tmp
end
code[wj_, x_] := N[(wj - N[(N[(N[(wj * N[Exp[wj], $MachinePrecision]), $MachinePrecision] - x), $MachinePrecision] / N[(N[Exp[wj], $MachinePrecision] + N[(wj * N[Exp[wj], $MachinePrecision]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]
code[wj_, x_] := Block[{t$95$0 = N[(x / N[(N[Exp[wj], $MachinePrecision] * N[(wj + 1.0), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]}, Block[{t$95$1 = N[(wj * N[Exp[wj], $MachinePrecision]), $MachinePrecision]}, Block[{t$95$2 = N[(wj / N[(wj * wj + -1.0), $MachinePrecision]), $MachinePrecision]}, If[LessEqual[N[(wj + N[(N[(x - t$95$1), $MachinePrecision] / N[(N[Exp[wj], $MachinePrecision] + t$95$1), $MachinePrecision]), $MachinePrecision]), $MachinePrecision], 2e-10], N[(N[(wj * wj + N[(N[(N[Power[wj, 4.0], $MachinePrecision] - N[Power[wj, 3.0], $MachinePrecision]), $MachinePrecision] - N[Power[wj, 5.0], $MachinePrecision]), $MachinePrecision]), $MachinePrecision] + t$95$0), $MachinePrecision], N[(t$95$0 + N[(N[(wj * 1.0 + N[(t$95$2 * N[(1.0 - wj), $MachinePrecision]), $MachinePrecision]), $MachinePrecision] + N[(N[(1.0 - wj), $MachinePrecision] * t$95$2 + N[(N[(wj + -1.0), $MachinePrecision] * t$95$2), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]]]]]
wj - \frac{wj \cdot e^{wj} - x}{e^{wj} + wj \cdot e^{wj}}
\begin{array}{l}
t_0 := \frac{x}{e^{wj} \cdot \left(wj + 1\right)}\\
t_1 := wj \cdot e^{wj}\\
t_2 := \frac{wj}{\mathsf{fma}\left(wj, wj, -1\right)}\\
\mathbf{if}\;wj + \frac{x - t_1}{e^{wj} + t_1} \leq 2 \cdot 10^{-10}:\\
\;\;\;\;\mathsf{fma}\left(wj, wj, \left({wj}^{4} - {wj}^{3}\right) - {wj}^{5}\right) + t_0\\

\mathbf{else}:\\
\;\;\;\;t_0 + \left(\mathsf{fma}\left(wj, 1, t_2 \cdot \left(1 - wj\right)\right) + \mathsf{fma}\left(1 - wj, t_2, \left(wj + -1\right) \cdot t_2\right)\right)\\


\end{array}

Error

Target

Original13.2
Target12.6
Herbie0.2
\[wj - \left(\frac{wj}{wj + 1} - \frac{x}{e^{wj} + wj \cdot e^{wj}}\right) \]

Derivation

  1. Split input into 2 regimes
  2. if (-.f64 wj (/.f64 (-.f64 (*.f64 wj (exp.f64 wj)) x) (+.f64 (exp.f64 wj) (*.f64 wj (exp.f64 wj))))) < 2.00000000000000007e-10

    1. Initial program 17.2

      \[wj - \frac{wj \cdot e^{wj} - x}{e^{wj} + wj \cdot e^{wj}} \]
    2. Simplified17.2

      \[\leadsto \color{blue}{wj - \frac{wj - \frac{x}{e^{wj}}}{wj + 1}} \]
      Proof
      (-.f64 wj (/.f64 (-.f64 wj (/.f64 x (exp.f64 wj))) (+.f64 wj 1))): 0 points increase in error, 0 points decrease in error
      (-.f64 wj (Rewrite=> div-sub_binary64 (-.f64 (/.f64 wj (+.f64 wj 1)) (/.f64 (/.f64 x (exp.f64 wj)) (+.f64 wj 1))))): 0 points increase in error, 0 points decrease in error
      (-.f64 wj (-.f64 (Rewrite<= *-rgt-identity_binary64 (*.f64 (/.f64 wj (+.f64 wj 1)) 1)) (/.f64 (/.f64 x (exp.f64 wj)) (+.f64 wj 1)))): 0 points increase in error, 0 points decrease in error
      (-.f64 wj (-.f64 (*.f64 (/.f64 wj (+.f64 wj 1)) (Rewrite<= *-inverses_binary64 (/.f64 (exp.f64 wj) (exp.f64 wj)))) (/.f64 (/.f64 x (exp.f64 wj)) (+.f64 wj 1)))): 3 points increase in error, 0 points decrease in error
      (-.f64 wj (-.f64 (Rewrite<= times-frac_binary64 (/.f64 (*.f64 wj (exp.f64 wj)) (*.f64 (+.f64 wj 1) (exp.f64 wj)))) (/.f64 (/.f64 x (exp.f64 wj)) (+.f64 wj 1)))): 1 points increase in error, 0 points decrease in error
      (-.f64 wj (-.f64 (/.f64 (*.f64 wj (exp.f64 wj)) (Rewrite<= distribute-rgt1-in_binary64 (+.f64 (exp.f64 wj) (*.f64 wj (exp.f64 wj))))) (/.f64 (/.f64 x (exp.f64 wj)) (+.f64 wj 1)))): 1 points increase in error, 0 points decrease in error
      (-.f64 wj (-.f64 (/.f64 (*.f64 wj (exp.f64 wj)) (+.f64 (exp.f64 wj) (*.f64 wj (exp.f64 wj)))) (Rewrite=> associate-/l/_binary64 (/.f64 x (*.f64 (+.f64 wj 1) (exp.f64 wj)))))): 0 points increase in error, 1 points decrease in error
      (-.f64 wj (-.f64 (/.f64 (*.f64 wj (exp.f64 wj)) (+.f64 (exp.f64 wj) (*.f64 wj (exp.f64 wj)))) (/.f64 x (Rewrite<= distribute-rgt1-in_binary64 (+.f64 (exp.f64 wj) (*.f64 wj (exp.f64 wj))))))): 0 points increase in error, 0 points decrease in error
      (-.f64 wj (Rewrite<= div-sub_binary64 (/.f64 (-.f64 (*.f64 wj (exp.f64 wj)) x) (+.f64 (exp.f64 wj) (*.f64 wj (exp.f64 wj)))))): 0 points increase in error, 0 points decrease in error
    3. Applied egg-rr9.0

      \[\leadsto \color{blue}{\left(wj - \frac{wj}{wj + 1}\right) + \frac{x}{\left(wj + 1\right) \cdot e^{wj}}} \]
    4. Taylor expanded in wj around 0 0.2

      \[\leadsto \color{blue}{\left({wj}^{2} + \left(-1 \cdot {wj}^{5} + \left(-1 \cdot {wj}^{3} + {wj}^{4}\right)\right)\right)} + \frac{x}{\left(wj + 1\right) \cdot e^{wj}} \]
    5. Simplified0.2

      \[\leadsto \color{blue}{\mathsf{fma}\left(wj, wj, \left({wj}^{4} - {wj}^{3}\right) - {wj}^{5}\right)} + \frac{x}{\left(wj + 1\right) \cdot e^{wj}} \]
      Proof
      (fma.f64 wj wj (-.f64 (-.f64 (pow.f64 wj 4) (pow.f64 wj 3)) (pow.f64 wj 5))): 0 points increase in error, 0 points decrease in error
      (fma.f64 wj wj (-.f64 (Rewrite<= unsub-neg_binary64 (+.f64 (pow.f64 wj 4) (neg.f64 (pow.f64 wj 3)))) (pow.f64 wj 5))): 0 points increase in error, 0 points decrease in error
      (fma.f64 wj wj (-.f64 (+.f64 (pow.f64 wj 4) (Rewrite<= mul-1-neg_binary64 (*.f64 -1 (pow.f64 wj 3)))) (pow.f64 wj 5))): 0 points increase in error, 0 points decrease in error
      (fma.f64 wj wj (-.f64 (Rewrite<= +-commutative_binary64 (+.f64 (*.f64 -1 (pow.f64 wj 3)) (pow.f64 wj 4))) (pow.f64 wj 5))): 0 points increase in error, 0 points decrease in error
      (fma.f64 wj wj (Rewrite<= unsub-neg_binary64 (+.f64 (+.f64 (*.f64 -1 (pow.f64 wj 3)) (pow.f64 wj 4)) (neg.f64 (pow.f64 wj 5))))): 0 points increase in error, 0 points decrease in error
      (fma.f64 wj wj (+.f64 (+.f64 (*.f64 -1 (pow.f64 wj 3)) (pow.f64 wj 4)) (Rewrite<= mul-1-neg_binary64 (*.f64 -1 (pow.f64 wj 5))))): 0 points increase in error, 0 points decrease in error
      (fma.f64 wj wj (Rewrite<= +-commutative_binary64 (+.f64 (*.f64 -1 (pow.f64 wj 5)) (+.f64 (*.f64 -1 (pow.f64 wj 3)) (pow.f64 wj 4))))): 0 points increase in error, 0 points decrease in error
      (Rewrite<= fma-def_binary64 (+.f64 (*.f64 wj wj) (+.f64 (*.f64 -1 (pow.f64 wj 5)) (+.f64 (*.f64 -1 (pow.f64 wj 3)) (pow.f64 wj 4))))): 1 points increase in error, 3 points decrease in error
      (+.f64 (Rewrite<= unpow2_binary64 (pow.f64 wj 2)) (+.f64 (*.f64 -1 (pow.f64 wj 5)) (+.f64 (*.f64 -1 (pow.f64 wj 3)) (pow.f64 wj 4)))): 0 points increase in error, 0 points decrease in error

    if 2.00000000000000007e-10 < (-.f64 wj (/.f64 (-.f64 (*.f64 wj (exp.f64 wj)) x) (+.f64 (exp.f64 wj) (*.f64 wj (exp.f64 wj)))))

    1. Initial program 2.1

      \[wj - \frac{wj \cdot e^{wj} - x}{e^{wj} + wj \cdot e^{wj}} \]
    2. Simplified0.2

      \[\leadsto \color{blue}{wj - \frac{wj - \frac{x}{e^{wj}}}{wj + 1}} \]
      Proof
      (-.f64 wj (/.f64 (-.f64 wj (/.f64 x (exp.f64 wj))) (+.f64 wj 1))): 0 points increase in error, 0 points decrease in error
      (-.f64 wj (Rewrite=> div-sub_binary64 (-.f64 (/.f64 wj (+.f64 wj 1)) (/.f64 (/.f64 x (exp.f64 wj)) (+.f64 wj 1))))): 0 points increase in error, 0 points decrease in error
      (-.f64 wj (-.f64 (Rewrite<= *-rgt-identity_binary64 (*.f64 (/.f64 wj (+.f64 wj 1)) 1)) (/.f64 (/.f64 x (exp.f64 wj)) (+.f64 wj 1)))): 0 points increase in error, 0 points decrease in error
      (-.f64 wj (-.f64 (*.f64 (/.f64 wj (+.f64 wj 1)) (Rewrite<= *-inverses_binary64 (/.f64 (exp.f64 wj) (exp.f64 wj)))) (/.f64 (/.f64 x (exp.f64 wj)) (+.f64 wj 1)))): 3 points increase in error, 0 points decrease in error
      (-.f64 wj (-.f64 (Rewrite<= times-frac_binary64 (/.f64 (*.f64 wj (exp.f64 wj)) (*.f64 (+.f64 wj 1) (exp.f64 wj)))) (/.f64 (/.f64 x (exp.f64 wj)) (+.f64 wj 1)))): 1 points increase in error, 0 points decrease in error
      (-.f64 wj (-.f64 (/.f64 (*.f64 wj (exp.f64 wj)) (Rewrite<= distribute-rgt1-in_binary64 (+.f64 (exp.f64 wj) (*.f64 wj (exp.f64 wj))))) (/.f64 (/.f64 x (exp.f64 wj)) (+.f64 wj 1)))): 1 points increase in error, 0 points decrease in error
      (-.f64 wj (-.f64 (/.f64 (*.f64 wj (exp.f64 wj)) (+.f64 (exp.f64 wj) (*.f64 wj (exp.f64 wj)))) (Rewrite=> associate-/l/_binary64 (/.f64 x (*.f64 (+.f64 wj 1) (exp.f64 wj)))))): 0 points increase in error, 1 points decrease in error
      (-.f64 wj (-.f64 (/.f64 (*.f64 wj (exp.f64 wj)) (+.f64 (exp.f64 wj) (*.f64 wj (exp.f64 wj)))) (/.f64 x (Rewrite<= distribute-rgt1-in_binary64 (+.f64 (exp.f64 wj) (*.f64 wj (exp.f64 wj))))))): 0 points increase in error, 0 points decrease in error
      (-.f64 wj (Rewrite<= div-sub_binary64 (/.f64 (-.f64 (*.f64 wj (exp.f64 wj)) x) (+.f64 (exp.f64 wj) (*.f64 wj (exp.f64 wj)))))): 0 points increase in error, 0 points decrease in error
    3. Applied egg-rr0.2

      \[\leadsto \color{blue}{\left(wj - \frac{wj}{wj + 1}\right) + \frac{x}{\left(wj + 1\right) \cdot e^{wj}}} \]
    4. Applied egg-rr0.2

      \[\leadsto \color{blue}{\left(\mathsf{fma}\left(wj, 1, -\left(wj + -1\right) \cdot \frac{wj}{\mathsf{fma}\left(wj, wj, -1\right)}\right) + \mathsf{fma}\left(-\left(wj + -1\right), \frac{wj}{\mathsf{fma}\left(wj, wj, -1\right)}, \left(wj + -1\right) \cdot \frac{wj}{\mathsf{fma}\left(wj, wj, -1\right)}\right)\right)} + \frac{x}{\left(wj + 1\right) \cdot e^{wj}} \]
  3. Recombined 2 regimes into one program.
  4. Final simplification0.2

    \[\leadsto \begin{array}{l} \mathbf{if}\;wj + \frac{x - wj \cdot e^{wj}}{e^{wj} + wj \cdot e^{wj}} \leq 2 \cdot 10^{-10}:\\ \;\;\;\;\mathsf{fma}\left(wj, wj, \left({wj}^{4} - {wj}^{3}\right) - {wj}^{5}\right) + \frac{x}{e^{wj} \cdot \left(wj + 1\right)}\\ \mathbf{else}:\\ \;\;\;\;\frac{x}{e^{wj} \cdot \left(wj + 1\right)} + \left(\mathsf{fma}\left(wj, 1, \frac{wj}{\mathsf{fma}\left(wj, wj, -1\right)} \cdot \left(1 - wj\right)\right) + \mathsf{fma}\left(1 - wj, \frac{wj}{\mathsf{fma}\left(wj, wj, -1\right)}, \left(wj + -1\right) \cdot \frac{wj}{\mathsf{fma}\left(wj, wj, -1\right)}\right)\right)\\ \end{array} \]

Alternatives

Alternative 1
Error0.2
Cost53252
\[\begin{array}{l} t_0 := wj \cdot e^{wj}\\ \mathbf{if}\;wj + \frac{x - t_0}{e^{wj} + t_0} \leq 2 \cdot 10^{-10}:\\ \;\;\;\;\mathsf{fma}\left(wj, wj, \left({wj}^{4} - {wj}^{3}\right) - {wj}^{5}\right) + \frac{x}{e^{wj} \cdot \left(wj + 1\right)}\\ \mathbf{else}:\\ \;\;\;\;\mathsf{fma}\left(wj - \frac{x}{e^{wj}}, \frac{-1}{wj + 1}, wj\right)\\ \end{array} \]
Alternative 2
Error0.7
Cost46468
\[\begin{array}{l} t_0 := wj \cdot e^{wj}\\ \mathbf{if}\;wj + \frac{x - t_0}{e^{wj} + t_0} \leq 2 \cdot 10^{-10}:\\ \;\;\;\;x + \mathsf{fma}\left(wj, wj, \left({wj}^{4} - {wj}^{3}\right) - {wj}^{5}\right)\\ \mathbf{else}:\\ \;\;\;\;\mathsf{fma}\left(wj - \frac{x}{e^{wj}}, \frac{-1}{wj + 1}, wj\right)\\ \end{array} \]
Alternative 3
Error0.7
Cost39876
\[\begin{array}{l} t_0 := wj \cdot e^{wj}\\ \mathbf{if}\;wj + \frac{x - t_0}{e^{wj} + t_0} \leq 2 \cdot 10^{-10}:\\ \;\;\;\;x + \mathsf{fma}\left(wj, wj, {wj}^{4} - {wj}^{3}\right)\\ \mathbf{else}:\\ \;\;\;\;\mathsf{fma}\left(wj - \frac{x}{e^{wj}}, \frac{-1}{wj + 1}, wj\right)\\ \end{array} \]
Alternative 4
Error1.1
Cost13508
\[\begin{array}{l} \mathbf{if}\;wj \leq 1.38 \cdot 10^{-5}:\\ \;\;\;\;\left(wj \cdot wj - \left(\left(wj \cdot x\right) \cdot 2 - x\right)\right) - {wj}^{3}\\ \mathbf{else}:\\ \;\;\;\;wj \cdot \left(1 - e^{wj - \left(wj + \mathsf{log1p}\left(wj\right)\right)}\right)\\ \end{array} \]
Alternative 5
Error1.1
Cost7428
\[\begin{array}{l} \mathbf{if}\;wj \leq 1.38 \cdot 10^{-5}:\\ \;\;\;\;\left(wj \cdot wj - \left(\left(wj \cdot x\right) \cdot 2 - x\right)\right) - {wj}^{3}\\ \mathbf{else}:\\ \;\;\;\;wj - \frac{wj}{wj + 1}\\ \end{array} \]
Alternative 6
Error1.0
Cost7236
\[\begin{array}{l} \mathbf{if}\;wj \leq 1.38 \cdot 10^{-5}:\\ \;\;\;\;\frac{x}{e^{wj} \cdot \left(wj + 1\right)} + wj \cdot wj\\ \mathbf{else}:\\ \;\;\;\;wj - \frac{wj}{wj + 1}\\ \end{array} \]
Alternative 7
Error1.7
Cost580
\[\begin{array}{l} \mathbf{if}\;wj \leq 1.08 \cdot 10^{-5}:\\ \;\;\;\;x + wj \cdot wj\\ \mathbf{else}:\\ \;\;\;\;wj - \frac{wj}{wj + 1}\\ \end{array} \]
Alternative 8
Error2.4
Cost320
\[x + wj \cdot wj \]
Alternative 9
Error61.2
Cost64
\[wj \]
Alternative 10
Error9.3
Cost64
\[x \]

Error

Reproduce

herbie shell --seed 2022329 
(FPCore (wj x)
  :name "Jmat.Real.lambertw, newton loop step"
  :precision binary64

  :herbie-target
  (- wj (- (/ wj (+ wj 1.0)) (/ x (+ (exp wj) (* wj (exp wj))))))

  (- wj (/ (- (* wj (exp wj)) x) (+ (exp wj) (* wj (exp wj))))))