Average Error: 61.3 → 0.5
Time: 22.1s
Precision: 64
\[-1 \lt x \land x \lt 1\]
\[\frac{\log \left(1 - x\right)}{\log \left(1 + x\right)}\]
↓
\[\frac{\log 1 - \left(1 \cdot x + \left(\frac{x}{1} \cdot \frac{x}{1}\right) \cdot \frac{1}{2}\right)}{\left(1 \cdot x - \left(\frac{x}{1} \cdot \frac{x}{1}\right) \cdot \frac{1}{2}\right) + \log 1}\]
\frac{\log \left(1 - x\right)}{\log \left(1 + x\right)}
↓
\frac{\log 1 - \left(1 \cdot x + \left(\frac{x}{1} \cdot \frac{x}{1}\right) \cdot \frac{1}{2}\right)}{\left(1 \cdot x - \left(\frac{x}{1} \cdot \frac{x}{1}\right) \cdot \frac{1}{2}\right) + \log 1}
double f(double x) {
        double r3987036 = 1.0;
        double r3987037 = x;
        double r3987038 = r3987036 - r3987037;
        double r3987039 = log(r3987038);
        double r3987040 = r3987036 + r3987037;
        double r3987041 = log(r3987040);
        double r3987042 = r3987039 / r3987041;
        return r3987042;
}
↓
double f(double x) {
        double r3987043 = 1.0;
        double r3987044 = log(r3987043);
        double r3987045 = x;
        double r3987046 = r3987043 * r3987045;
        double r3987047 = r3987045 / r3987043;
        double r3987048 = r3987047 * r3987047;
        double r3987049 = 0.5;
        double r3987050 = r3987048 * r3987049;
        double r3987051 = r3987046 + r3987050;
        double r3987052 = r3987044 - r3987051;
        double r3987053 = r3987046 - r3987050;
        double r3987054 = r3987053 + r3987044;
        double r3987055 = r3987052 / r3987054;
        return r3987055;
}

Error

Bits error versus x

Try it out

Your Program's Arguments

Results

Enter valid numbers for all inputs

Target

Original61.3
Target0.4
Herbie0.5
\[-\left(\left(\left(1 + x\right) + \frac{x \cdot x}{2}\right) + 0.4166666666666666851703837437526090070605 \cdot {x}^{3}\right)\]

Derivation

  1. Initial program 61.3

    \[\frac{\log \left(1 - x\right)}{\log \left(1 + x\right)}\]

  2. Taylor expanded around 0 60.5

    \[\leadsto \frac{\log \left(1 - x\right)}{\color{blue}{\left(\log 1 + 1 \cdot x\right) - \frac{1}{2} \cdot \frac{{x}^{2}}{{1}^{2}}}}\]

  3. Simplified60.5

    \[\leadsto \frac{\log \left(1 - x\right)}{\color{blue}{\log 1 + \left(1 \cdot x - \frac{1}{2} \cdot \left(\frac{x}{1} \cdot \frac{x}{1}\right)\right)}}\]

  4. Taylor expanded around 0 0.5

    \[\leadsto \frac{\color{blue}{\log 1 - \left(1 \cdot x + \frac{1}{2} \cdot \frac{{x}^{2}}{{1}^{2}}\right)}}{\log 1 + \left(1 \cdot x - \frac{1}{2} \cdot \left(\frac{x}{1} \cdot \frac{x}{1}\right)\right)}\]

  5. Simplified0.5

    \[\leadsto \frac{\color{blue}{\log 1 - \left(1 \cdot x + \left(\frac{x}{1} \cdot \frac{x}{1}\right) \cdot \frac{1}{2}\right)}}{\log 1 + \left(1 \cdot x - \frac{1}{2} \cdot \left(\frac{x}{1} \cdot \frac{x}{1}\right)\right)}\]

  6. Final simplification0.5

    \[\leadsto \frac{\log 1 - \left(1 \cdot x + \left(\frac{x}{1} \cdot \frac{x}{1}\right) \cdot \frac{1}{2}\right)}{\left(1 \cdot x - \left(\frac{x}{1} \cdot \frac{x}{1}\right) \cdot \frac{1}{2}\right) + \log 1}\]

Reproduce

herbie shell --seed 2019172 
(FPCore (x)
  :name "qlog (example 3.10)"
  :pre (and (< -1.0 x) (< x 1.0))

  :herbie-target
  (- (+ (+ (+ 1.0 x) (/ (* x x) 2.0)) (* 0.4166666666666667 (pow x 3.0))))

  (/ (log (- 1.0 x)) (log (+ 1.0 x))))