\[2 \cdot \cos \left(\frac{2 \cdot \pi}{3} + \frac{\cos^{-1} \left(\frac{-g}{h}\right)}{3}\right)\]
2 \cdot \cos \left(\frac{2 \cdot \pi}{3} + \frac{\cos^{-1} \left(\frac{-g}{h}\right)}{3}\right)
(FPCore (g h)
 :precision binary64
 (* 2.0 (cos (+ (/ (* 2.0 PI) 3.0) (/ (acos (/ (- g) h)) 3.0)))))
double code(double g, double h) {
	return 2.0 * cos(((2.0 * ((double) M_PI)) / 3.0) + (acos(-g / h) / 3.0));
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2021096 
(FPCore (g h)
  :name "2-ancestry mixing, negative discriminant"
  :precision binary64
  (* 2.0 (cos (+ (/ (* 2.0 PI) 3.0) (/ (acos (/ (- g) h)) 3.0)))))

Backtrace

...src/sampling.rkt:193:4: arity mismatch; the expected number of arguments does not match the given number expected: 1 given: 0LC
loop/data/pavpan/nightlies/herbie/test-filtered-on-examples/src/points.rkt1004
prepare-points/data/pavpan/nightlies/herbie/test-filtered-on-examples/src/points.rkt1310
run-improve/data/pavpan/nightlies/herbie/test-filtered-on-examples/src/mainloop.rkt3950
(unnamed)/data/pavpan/nightlies/herbie/test-filtered-on-examples/src/sandbox.rkt546
run/opt/racket-7.9/share/pkgs/profile-lib/main.rkt392
profile-thunk/opt/racket-7.9/share/pkgs/profile-lib/main.rkt90
(unnamed)/opt/racket-7.9/collects/racket/engine.rkt4224