\[2 \cdot \cos \left(\frac{2 \cdot \pi}{3} + \frac{\cos^{-1} \left(\frac{-g}{h}\right)}{3}\right)\]

2 \cdot \cos \left(\frac{2 \cdot \pi}{3} + \frac{\cos^{-1} \left(\frac{-g}{h}\right)}{3}\right)

double f(double g, double h) {
        double r112144 = 2.0;
        double r112145 = atan2(1.0, 0.0);
        double r112146 = r112144 * r112145;
        double r112147 = 3.0;
        double r112148 = r112146 / r112147;
        double r112149 = g;
        double r112150 = -r112149;
        double r112151 = h;
        double r112152 = r112150 / r112151;
        double r112153 = acos(r112152);
        double r112154 = r112153 / r112147;
        double r112155 = r112148 + r112154;
        double r112156 = cos(r112155);
        double r112157 = r112144 * r112156;
        return r112157;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019323 
(FPCore (g h)
  :name "2-ancestry mixing, negative discriminant"
  :precision binary64
  (* 2 (cos (+ (/ (* 2 PI) 3) (/ (acos (/ (- g) h)) 3)))))

Backtrace

get-representation: Unknown representation real		L	C
(unnamed)	/data/pavpan/nightlies/herbie/fix-interface-bugs/src/core/regimes.rkt	65	3
filter	/opt/racket-7.2/collects/racket/private/list.rkt	256	2
infer-splitpoints	/data/pavpan/nightlies/herbie/fix-interface-bugs/src/core/regimes.rkt	34	0
get-final-combination	/data/pavpan/nightlies/herbie/fix-interface-bugs/src/mainloop.rkt	369	0
(unnamed)	/opt/racket-7.2/collects/racket/private/more-scheme.rkt	261	28
run	/opt/racket-7.2/share/pkgs/profile-lib/main.rkt	39	2
profile-thunk16	/opt/racket-7.2/share/pkgs/profile-lib/main.rkt	9	0
(unnamed)	/opt/racket-7.2/collects/racket/private/more-scheme.rkt	261	28