\[\lambda_1 + \tan^{-1}_* \frac{\cos \phi_2 \cdot \sin \left(\lambda_1 - \lambda_2\right)}{\cos \phi_1 + \cos \phi_2 \cdot \cos \left(\lambda_1 - \lambda_2\right)}\]

\lambda_1 + \tan^{-1}_* \frac{\cos \phi_2 \cdot \sin \left(\lambda_1 - \lambda_2\right)}{\cos \phi_1 + \cos \phi_2 \cdot \cos \left(\lambda_1 - \lambda_2\right)}

double f(double lambda1, double lambda2, double phi1, double phi2) {
        double r36059 = lambda1;
        double r36060 = phi2;
        double r36061 = cos(r36060);
        double r36062 = lambda2;
        double r36063 = r36059 - r36062;
        double r36064 = sin(r36063);
        double r36065 = r36061 * r36064;
        double r36066 = phi1;
        double r36067 = cos(r36066);
        double r36068 = cos(r36063);
        double r36069 = r36061 * r36068;
        double r36070 = r36067 + r36069;
        double r36071 = atan2(r36065, r36070);
        double r36072 = r36059 + r36071;
        return r36072;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019323 +o rules:numerics
(FPCore (lambda1 lambda2 phi1 phi2)
  :name "Midpoint on a great circle"
  :precision binary64
  (+ lambda1 (atan2 (* (cos phi2) (sin (- lambda1 lambda2))) (+ (cos phi1) (* (cos phi2) (cos (- lambda1 lambda2)))))))

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