Average Error: 29.5 → 1.0
Time: 18.2s
Precision: binary64
Cost: 19648
\[ \begin{array}{c}[a, b] = \mathsf{sort}([a, b])\\ \end{array} \]
\[\log \left(e^{a} + e^{b}\right) \]
\[\mathsf{log1p}\left(e^{a}\right) + \frac{b}{e^{a} + 1} \]
(FPCore (a b) :precision binary64 (log (+ (exp a) (exp b))))
(FPCore (a b) :precision binary64 (+ (log1p (exp a)) (/ b (+ (exp a) 1.0))))
double code(double a, double b) {
	return log((exp(a) + exp(b)));
}
double code(double a, double b) {
	return log1p(exp(a)) + (b / (exp(a) + 1.0));
}
public static double code(double a, double b) {
	return Math.log((Math.exp(a) + Math.exp(b)));
}
public static double code(double a, double b) {
	return Math.log1p(Math.exp(a)) + (b / (Math.exp(a) + 1.0));
}
def code(a, b):
	return math.log((math.exp(a) + math.exp(b)))
def code(a, b):
	return math.log1p(math.exp(a)) + (b / (math.exp(a) + 1.0))
function code(a, b)
	return log(Float64(exp(a) + exp(b)))
end
function code(a, b)
	return Float64(log1p(exp(a)) + Float64(b / Float64(exp(a) + 1.0)))
end
code[a_, b_] := N[Log[N[(N[Exp[a], $MachinePrecision] + N[Exp[b], $MachinePrecision]), $MachinePrecision]], $MachinePrecision]
code[a_, b_] := N[(N[Log[1 + N[Exp[a], $MachinePrecision]], $MachinePrecision] + N[(b / N[(N[Exp[a], $MachinePrecision] + 1.0), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]
\log \left(e^{a} + e^{b}\right)
\mathsf{log1p}\left(e^{a}\right) + \frac{b}{e^{a} + 1}

Error

Try it out

Your Program's Arguments

Results

Enter valid numbers for all inputs

Derivation

  1. Initial program 29.5

    \[\log \left(e^{a} + e^{b}\right) \]
  2. Taylor expanded in b around 0 1.1

    \[\leadsto \color{blue}{\log \left(1 + e^{a}\right) + \frac{b}{1 + e^{a}}} \]
  3. Simplified1.0

    \[\leadsto \color{blue}{\mathsf{log1p}\left(e^{a}\right) + \frac{b}{1 + e^{a}}} \]
    Proof
    (+.f64 (log1p.f64 (exp.f64 a)) (/.f64 b (+.f64 1 (exp.f64 a)))): 0 points increase in error, 0 points decrease in error
    (+.f64 (Rewrite<= log1p-def_binary64 (log.f64 (+.f64 1 (exp.f64 a)))) (/.f64 b (+.f64 1 (exp.f64 a)))): 4 points increase in error, 1 points decrease in error
  4. Final simplification1.0

    \[\leadsto \mathsf{log1p}\left(e^{a}\right) + \frac{b}{e^{a} + 1} \]

Alternatives

Alternative 1
Error2.5
Cost12992
\[\mathsf{log1p}\left(e^{a} + b\right) \]
Alternative 2
Error31.5
Cost12864
\[\mathsf{log1p}\left(e^{a}\right) \]
Alternative 3
Error32.2
Cost6720
\[b \cdot 0.5 + \log 2 \]
Alternative 4
Error32.3
Cost6592
\[\log \left(b + 2\right) \]
Alternative 5
Error32.6
Cost6464
\[\log 2 \]
Alternative 6
Error62.3
Cost192
\[a \cdot 0.5 \]

Error

Reproduce

herbie shell --seed 2022308 
(FPCore (a b)
  :name "symmetry log of sum of exp"
  :precision binary64
  (log (+ (exp a) (exp b))))