#include <iostream>
#include <cmath>

using namespace std;

// Some constants useful in solar system
#define mmoon 7.342e25           // Moon mass in g
#define mearth 5.97219e27        // Earth mass in g 
#define msun 1.989e33            // Sun mass in g 
#define au 1.495978707e13        // au in cm 
#define rearth 6371e5            // Earth dameter in cm 
#define dmoon 384400e5           // Distance moon in cm 
#define sec_per_year 3.1556926e7 // seconds per year 
#define parsec 3.085678e18       // cm per parsec
#define kparsec 3.085678e21      // cm per kilo parsec
#define mparsec 3.085678e24      // cm per mega parsec

// unit system of the simulation (solar system)
#define m_unit msun
#define l_unit au
#define t_unit sec_per_year     // Years

// unit system of the simulation (galaxies)
// #define m_unit 1e10*msun
// #define l_unit kparsec
// #define t_unit 1e6*sec_per_year // mega Years 

// unit system of the simulation (clusters)
// #define m_unit 1e10*msun
// #define l_unit kparsec
// #define t_unit 1e9*sec_per_year // giga Years 

// resulting velocity units
#define v_unit l_unit / t_unit

// Gravitational constant in internal units 
#define G 6.672e-8 * m_unit * t_unit * t_unit / l_unit / l_unit / l_unit

int main(int argc, const char **argv) {
    // Define the variables we need
    double dist, mass, acc, acc_cgs;

    // Lets output at the beginning some useful information ...
    cout << "Hallo World" << endl;
    cout << "My own unit system is: " << endl;
    cout << "L = " << l_unit << endl;
    cout << "T = " << t_unit << endl;
    cout << "M = " << m_unit << endl;
    cout << "V = " << v_unit << endl;

    cout << "Gravitational constant in my internal units is: " << endl;
    cout << "G = " << G << endl;

    // acc from earth
    cout << "Acceleration by earth:" << endl;
    dist = rearth / l_unit;
    mass = mearth / m_unit;
    acc = G * mass / (dist * dist);
    acc_cgs = acc * l_unit / (t_unit * t_unit);
    cout << "acc = " << acc << " [internal units] = " << acc_cgs << " [cm/s^2]" << endl;

    // acc from moon
    cout << "Acceleration by moon:" << endl;
    dist = (dmoon - rearth) / l_unit;    // here the size of earth could matter !
    mass = mmoon / m_unit;
    acc = G * mass / (dist * dist);
    acc_cgs = acc * l_unit / (t_unit * t_unit);
    cout << "acc = " << acc << " [internal units] = " << acc_cgs << " [cm/s^2]" << endl;

    // acc from moon
    cout << "Acceleration by sun:" << endl;
    dist = au / l_unit;
    mass = msun / m_unit;
    acc = G * mass / (dist * dist);
    acc_cgs = acc * l_unit / (t_unit * t_unit);
    cout << "acc = " << acc << " [internal units] = " << acc_cgs << " [cm/s^2]" << endl;

    // acc from galaxy
    cout << "Acceleration by galaxy:" << endl;
    dist = 8 * kparsec / l_unit;
    mass = 1e11 * msun / m_unit;
    acc = G * mass / (dist * dist);
    acc_cgs = acc * l_unit / (t_unit * t_unit);
    cout << "acc = " << acc << " [internal units] = " << acc_cgs << " [cm/s^2]" << endl;

    // acc from virgo cluster
    cout << "Acceleration by virgo:" << endl;
    dist = 10 * mparsec / l_unit;
    mass = 1e15 * msun / m_unit;
    acc = G * mass / (dist * dist);
    acc_cgs = acc * l_unit / (t_unit * t_unit);
    cout << "acc = " << acc << " [internal units] = " << acc_cgs << " [cm/s^2]" << endl;

    // acc of sun on pluto
    cout << "Acceleration of sun on pluto:" << endl;
    dist = 39.5 * au / l_unit;
    mass = msun / m_unit;
    acc = G * mass / (dist * dist);
    acc_cgs = acc * l_unit / (t_unit * t_unit);
    cout << "acc = " << acc << " [internal units] = " << acc_cgs << " [cm/s^2]" << endl;

    // acc of sun on voyager
    cout << "Acceleration of sun on voyager:" << endl;
    dist = 138 * au / l_unit;
    mass = msun / m_unit;
    acc = G * mass / (dist * dist);
    acc_cgs = acc * l_unit / (t_unit * t_unit);
    cout << "acc = " << acc << " [internal units] = " << acc_cgs << " [cm/s^2]" << endl;

    // acc on galaxy at border of a cluster
    cout << "Acceleration at border of a cluster:" << endl;
    dist = 2 * mparsec / l_unit;
    mass = 1e15 * msun / m_unit;
    acc = G * mass / (dist * dist);
    acc_cgs = acc * l_unit / (t_unit * t_unit);
    cout << "acc = " << acc << " [internal units] = " << acc_cgs << " [cm/s^2]" << endl;

    return 0;
}