System.Random.MWC.Distributions:truncatedExp from mwc-random-0.13.3.2

Average Error: 25.0 → 1.0

Time: 17.5s

Precision: binary64

Cost: 13248

Math

\[x - \frac{\log \left(\left(1 - y\right) + y \cdot e^{z}\right)}{t} \]

↓

\[x - \frac{\mathsf{log1p}\left(y \cdot \mathsf{expm1}\left(z\right)\right)}{t} \]

FPCore

(FPCore (x y z t)
 :precision binary64
 (- x (/ (log (+ (- 1.0 y) (* y (exp z)))) t)))

↓

(FPCore (x y z t) :precision binary64 (- x (/ (log1p (* y (expm1 z))) t)))

C

double code(double x, double y, double z, double t) {
	return x - (log(((1.0 - y) + (y * exp(z)))) / t);
}

↓

double code(double x, double y, double z, double t) {
	return x - (log1p((y * expm1(z))) / t);
}

Java

public static double code(double x, double y, double z, double t) {
	return x - (Math.log(((1.0 - y) + (y * Math.exp(z)))) / t);
}

↓

public static double code(double x, double y, double z, double t) {
	return x - (Math.log1p((y * Math.expm1(z))) / t);
}

Python

def code(x, y, z, t):
	return x - (math.log(((1.0 - y) + (y * math.exp(z)))) / t)

↓

def code(x, y, z, t):
	return x - (math.log1p((y * math.expm1(z))) / t)

Julia

function code(x, y, z, t)
	return Float64(x - Float64(log(Float64(Float64(1.0 - y) + Float64(y * exp(z)))) / t))
end

↓

function code(x, y, z, t)
	return Float64(x - Float64(log1p(Float64(y * expm1(z))) / t))
end

Wolfram

code[x_, y_, z_, t_] := N[(x - N[(N[Log[N[(N[(1.0 - y), $MachinePrecision] + N[(y * N[Exp[z], $MachinePrecision]), $MachinePrecision]), $MachinePrecision]], $MachinePrecision] / t), $MachinePrecision]), $MachinePrecision]

↓

code[x_, y_, z_, t_] := N[(x - N[(N[Log[1 + N[(y * N[(Exp[z] - 1), $MachinePrecision]), $MachinePrecision]], $MachinePrecision] / t), $MachinePrecision]), $MachinePrecision]

Target

Original	25.0
Target	16.2
Herbie	1.0

\[\begin{array}{l} \mathbf{if}\;z < -2.8874623088207947 \cdot 10^{+119}:\\ \;\;\;\;\left(x - \frac{\frac{-0.5}{y \cdot t}}{z \cdot z}\right) - \frac{-0.5}{y \cdot t} \cdot \frac{\frac{2}{z}}{z \cdot z}\\ \mathbf{else}:\\ \;\;\;\;x - \frac{\log \left(1 + z \cdot y\right)}{t}\\ \end{array} \]

Derivation

1. Initial program 25.0

   \[x - \frac{\log \left(\left(1 - y\right) + y \cdot e^{z}\right)}{t} \]

2. Simplified 1.0

   \[\leadsto \color{blue}{x - \frac{\mathsf{log1p}\left(y \cdot \mathsf{expm1}\left(z\right)\right)}{t}} \]
   Proof
   (-.f64 x (/.f64 (log1p.f64 (*.f64 y (expm1.f64 z))) t)): 0 points increase in error, 0 points decrease in error
   (-.f64 x (/.f64 (log1p.f64 (*.f64 y (Rewrite<= expm1-def_binary64 (-.f64 (exp.f64 z) 1)))) t)): 0 points increase in error, 0 points decrease in error
   (-.f64 x (/.f64 (log1p.f64 (*.f64 y (Rewrite=> sub-neg_binary64 (+.f64 (exp.f64 z) (neg.f64 1))))) t)): 0 points increase in error, 0 points decrease in error
   (-.f64 x (/.f64 (log1p.f64 (*.f64 y (+.f64 (exp.f64 z) (Rewrite=> metadata-eval -1)))) t)): 0 points increase in error, 0 points decrease in error
   (-.f64 x (/.f64 (log1p.f64 (Rewrite<= distribute-rgt-out_binary64 (+.f64 (*.f64 (exp.f64 z) y) (*.f64 -1 y)))) t)): 0 points increase in error, 0 points decrease in error
   (-.f64 x (/.f64 (log1p.f64 (+.f64 (*.f64 (exp.f64 z) y) (Rewrite<= neg-mul-1_binary64 (neg.f64 y)))) t)): 0 points increase in error, 0 points decrease in error
   (-.f64 x (/.f64 (log1p.f64 (+.f64 (Rewrite<= *-commutative_binary64 (*.f64 y (exp.f64 z))) (neg.f64 y))) t)): 0 points increase in error, 0 points decrease in error
   (-.f64 x (/.f64 (log1p.f64 (+.f64 (Rewrite<= remove-double-neg_binary64 (neg.f64 (neg.f64 (*.f64 y (exp.f64 z))))) (neg.f64 y))) t)): 0 points increase in error, 0 points decrease in error
   (-.f64 x (/.f64 (log1p.f64 (Rewrite<= distribute-neg-in_binary64 (neg.f64 (+.f64 (neg.f64 (*.f64 y (exp.f64 z))) y)))) t)): 0 points increase in error, 0 points decrease in error
   (-.f64 x (/.f64 (log1p.f64 (neg.f64 (Rewrite<= +-commutative_binary64 (+.f64 y (neg.f64 (*.f64 y (exp.f64 z))))))) t)): 0 points increase in error, 0 points decrease in error
   (-.f64 x (/.f64 (log1p.f64 (neg.f64 (Rewrite<= sub-neg_binary64 (-.f64 y (*.f64 y (exp.f64 z)))))) t)): 0 points increase in error, 0 points decrease in error
   (-.f64 x (/.f64 (Rewrite<= log1p-def_binary64 (log.f64 (+.f64 1 (neg.f64 (-.f64 y (*.f64 y (exp.f64 z))))))) t)): 0 points increase in error, 0 points decrease in error
   (-.f64 x (/.f64 (log.f64 (Rewrite<= sub-neg_binary64 (-.f64 1 (-.f64 y (*.f64 y (exp.f64 z)))))) t)): 0 points increase in error, 0 points decrease in error
   (-.f64 x (/.f64 (log.f64 (Rewrite<= associate-+l-_binary64 (+.f64 (-.f64 1 y) (*.f64 y (exp.f64 z))))) t)): 18 points increase in error, 0 points decrease in error
   (-.f64 x (Rewrite<= *-lft-identity_binary64 (*.f64 1 (/.f64 (log.f64 (+.f64 (-.f64 1 y) (*.f64 y (exp.f64 z)))) t)))): 0 points increase in error, 18 points decrease in error
   (-.f64 (Rewrite<= *-lft-identity_binary64 (*.f64 1 x)) (*.f64 1 (/.f64 (log.f64 (+.f64 (-.f64 1 y) (*.f64 y (exp.f64 z)))) t))): 0 points increase in error, 0 points decrease in error
   (Rewrite=> distribute-lft-out--_binary64 (*.f64 1 (-.f64 x (/.f64 (log.f64 (+.f64 (-.f64 1 y) (*.f64 y (exp.f64 z)))) t)))): 0 points increase in error, 0 points decrease in error
   (Rewrite=> *-lft-identity_binary64 (-.f64 x (/.f64 (log.f64 (+.f64 (-.f64 1 y) (*.f64 y (exp.f64 z)))) t))): 17 points increase in error, 0 points decrease in error

3. Final simplification 1.0

   \[\leadsto x - \frac{\mathsf{log1p}\left(y \cdot \mathsf{expm1}\left(z\right)\right)}{t} \]

Alternatives

Alternative 1
Error	6.5
Cost	7232

\[x - \frac{1}{\frac{t}{y \cdot \mathsf{expm1}\left(z\right)} + t \cdot 0.5} \]

Alternative 2
Error	6.7
Cost	6980

\[\begin{array}{l} \mathbf{if}\;y \leq -1.66 \cdot 10^{+16}:\\ \;\;\;\;x - \frac{1}{t \cdot 0.5 + \frac{t}{y \cdot z}}\\ \mathbf{else}:\\ \;\;\;\;x - y \cdot \frac{\mathsf{expm1}\left(z\right)}{t}\\ \end{array} \]

Alternative 3
Error	9.4
Cost	1220

\[\begin{array}{l} \mathbf{if}\;z \leq -2 \cdot 10^{-172}:\\ \;\;\;\;x - \frac{1}{\frac{\frac{t}{z}}{y} + 0.5 \cdot \left(t - \frac{t}{y}\right)}\\ \mathbf{else}:\\ \;\;\;\;x - \frac{1}{t \cdot 0.5 + \frac{t}{y \cdot z}}\\ \end{array} \]

Alternative 4
Error	10.4
Cost	964

\[\begin{array}{l} \mathbf{if}\;z \leq -2.85 \cdot 10^{+48}:\\ \;\;\;\;x\\ \mathbf{else}:\\ \;\;\;\;x - \frac{1}{t \cdot 0.5 + \frac{t}{y \cdot z}}\\ \end{array} \]

Alternative 5
Error	11.3
Cost	580

\[\begin{array}{l} \mathbf{if}\;z \leq -7.5 \cdot 10^{+20}:\\ \;\;\;\;x\\ \mathbf{else}:\\ \;\;\;\;x - y \cdot \frac{z}{t}\\ \end{array} \]

Alternative 6
Error	18.2
Cost	64

\[x \]

Reproduce

herbie shell --seed 2022343 
(FPCore (x y z t)
  :name "System.Random.MWC.Distributions:truncatedExp from mwc-random-0.13.3.2"
  :precision binary64

  :herbie-target
  (if (< z -2.8874623088207947e+119) (- (- x (/ (/ (- 0.5) (* y t)) (* z z))) (* (/ (- 0.5) (* y t)) (/ (/ 2.0 z) (* z z)))) (- x (/ (log (+ 1.0 (* z y))) t)))

  (- x (/ (log (+ (- 1.0 y) (* y (exp z)))) t)))