\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{\left(\sin \lambda_1 \cdot \cos \lambda_2\right) \cdot \cos \phi_2 + \left(\cos \lambda_1 \cdot \sin \left(-\lambda_2\right)\right) \cdot \cos \phi_2}{\sqrt[3]{\left(\left(\left(\cos \lambda_1 \cdot \cos \lambda_2 + \sin \lambda_1 \cdot \sin \lambda_2\right) \cdot \cos \phi_2 + \cos \phi_1\right) \cdot \left(\left(\cos \lambda_1 \cdot \cos \lambda_2 + \sin \lambda_1 \cdot \sin \lambda_2\right) \cdot \cos \phi_2 + \cos \phi_1\right)\right) \cdot \left(\left(\cos \lambda_1 \cdot \cos \lambda_2 + \sin \lambda_1 \cdot \sin \lambda_2\right) \cdot \cos \phi_2 + \cos \phi_1\right)}}double f(double lambda1, double lambda2, double phi1, double phi2) {
double r43002 = lambda1;
double r43003 = phi2;
double r43004 = cos(r43003);
double r43005 = lambda2;
double r43006 = r43002 - r43005;
double r43007 = sin(r43006);
double r43008 = r43004 * r43007;
double r43009 = phi1;
double r43010 = cos(r43009);
double r43011 = cos(r43006);
double r43012 = r43004 * r43011;
double r43013 = r43010 + r43012;
double r43014 = atan2(r43008, r43013);
double r43015 = r43002 + r43014;
return r43015;
}
double f(double lambda1, double lambda2, double phi1, double phi2) {
double r43016 = lambda1;
double r43017 = sin(r43016);
double r43018 = lambda2;
double r43019 = cos(r43018);
double r43020 = r43017 * r43019;
double r43021 = phi2;
double r43022 = cos(r43021);
double r43023 = r43020 * r43022;
double r43024 = cos(r43016);
double r43025 = -r43018;
double r43026 = sin(r43025);
double r43027 = r43024 * r43026;
double r43028 = r43027 * r43022;
double r43029 = r43023 + r43028;
double r43030 = r43024 * r43019;
double r43031 = sin(r43018);
double r43032 = r43017 * r43031;
double r43033 = r43030 + r43032;
double r43034 = r43033 * r43022;
double r43035 = phi1;
double r43036 = cos(r43035);
double r43037 = r43034 + r43036;
double r43038 = r43037 * r43037;
double r43039 = r43038 * r43037;
double r43040 = cbrt(r43039);
double r43041 = atan2(r43029, r43040);
double r43042 = r43016 + r43041;
return r43042;
}



Bits error versus lambda1



Bits error versus lambda2



Bits error versus phi1



Bits error versus phi2
Results
Initial program 0.8
rmApplied sub-neg0.8
Applied cos-sum0.8
Simplified0.8
rmApplied sub-neg0.8
Applied sin-sum0.2
Applied distribute-lft-in0.2
Simplified0.2
Simplified0.2
rmApplied add-cbrt-cube0.3
Simplified0.3
rmApplied add-cbrt-cube0.3
Applied rem-cube-cbrt0.3
Final simplification0.3
herbie shell --seed 2019195
(FPCore (lambda1 lambda2 phi1 phi2)
:name "Midpoint on a great circle"
(+ lambda1 (atan2 (* (cos phi2) (sin (- lambda1 lambda2))) (+ (cos phi1) (* (cos phi2) (cos (- lambda1 lambda2)))))))