Cubic critical, medium range

Average Error: 43.7 → 12.1

Time: 11.8s

Precision: 64

\[1.1102230246251565404236316680908203125 \cdot 10^{-16} \lt a \lt 9007199254740992 \land 1.1102230246251565404236316680908203125 \cdot 10^{-16} \lt b \lt 9007199254740992 \land 1.1102230246251565404236316680908203125 \cdot 10^{-16} \lt c \lt 9007199254740992\]

Math

\[\frac{\left(-b\right) + \sqrt{b \cdot b - \left(3 \cdot a\right) \cdot c}}{3 \cdot a}\]

↓

\[-0.5 \cdot \frac{c}{b}\]

C

double f(double a, double b, double c) {
        double r42075 = b;
        double r42076 = -r42075;
        double r42077 = r42075 * r42075;
        double r42078 = 3.0;
        double r42079 = a;
        double r42080 = r42078 * r42079;
        double r42081 = c;
        double r42082 = r42080 * r42081;
        double r42083 = r42077 - r42082;
        double r42084 = sqrt(r42083);
        double r42085 = r42076 + r42084;
        double r42086 = r42085 / r42080;
        return r42086;
}

↓

double f(double __attribute__((unused)) a, double b, double c) {
        double r42087 = -0.5;
        double r42088 = c;
        double r42089 = b;
        double r42090 = r42088 / r42089;
        double r42091 = r42087 * r42090;
        return r42091;
}

Error

Bits error versus a

Bits error versus b

Bits error versus c

Derivation

1. Initial program 43.7

   \[\frac{\left(-b\right) + \sqrt{b \cdot b - \left(3 \cdot a\right) \cdot c}}{3 \cdot a}\]

2. Simplified 43.7

   \[\leadsto \color{blue}{\frac{\sqrt{b \cdot b - \left(3 \cdot a\right) \cdot c} - b}{3 \cdot a}}\]

3. Taylor expanded around inf 12.1

   \[\leadsto \color{blue}{-0.5 \cdot \frac{c}{b}}\]

4. Final simplification 12.1

   \[\leadsto -0.5 \cdot \frac{c}{b}\]

Reproduce

herbie shell --seed 2019325 +o rules:numerics
(FPCore (a b c)
  :name "Cubic critical, medium range"
  :precision binary64
  :pre (and (< 1.11022e-16 a 9.0072e+15) (< 1.11022e-16 b 9.0072e+15) (< 1.11022e-16 c 9.0072e+15))
  (/ (+ (- b) (sqrt (- (* b b) (* (* 3 a) c)))) (* 3 a)))