get_gravity.cpp

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// C/C++ headers
#include <cmath>
#include <cstring>
#include <sstream>
#include <stdexcept>
 
double GetGravity(char const *planet, double pclat) {
  std::stringstream msg;
  double g_new;
 
  if (strcmp(planet, "Jupiter") == 0) {
    double grav = 23.3;
    double S = sin(pclat * M_PI / 180.);
    double SS = S * S;
    double CS = S * sqrt(1 - SS);
    double GR =
        -grav +
        SS * (-4.26594 +
              SS * (0.47685 +
                    SS * (-0.100513 + SS * (0.0237067 - 0.00305515 * SS))));
    double GTH =
        CS * (-3.42313 +
              SS * (0.119119 +
                    SS * (0.00533106 + SS * (-0.00647658 + SS * 0.000785945))));
    g_new = sqrt(GR * GR + GTH * GTH);
  } else if (strcmp(planet, "Saturn")) {
    double S = sin(pclat * M_PI / 180.);
    double SS = S * S;
    double CS = S * sqrt(1 - SS);
    double GR =
        -9.06656 +
        SS * (-3.59253 +
              SS * (0.704538 +
                    SS * (-0.260158 + SS * (0.0923098 - SS * 0.0166287))));
    double GTH =
        CS * (-2.25384 +
              SS * (.152112 +
                    SS * (-.0102391 + SS * (-.00714765 + SS * .000865634))));
    g_new = sqrt(GR * GR + GTH * GTH);
  } else {
    msg << "### FATAL ERROR in planet_gravity" << std::endl
        << "Name of the planet not recognized" << std::endl
        << "Choose from [Jupiter|Saturn]" << std::endl;
    throw std::runtime_error(msg.str().c_str());
  }
 
  return g_new;
}