inline real get_r2(const vec3 &pos)
{
#ifndef _CYLINDER_
return pos.norm2();
#else
return sqr(pos.x) + sqr(pos.y);
#endif
}
const std::pair<vec3, real> gacc(const vec3 &pos)
{
const real ds2 = pos.norm2();
const real ds = std::sqrt(ds2);
const real ids = (ds > 0.0) ? 1.0/ds : 0.0;
const real ids2 = ids*ids;
const real gravity_mass = GM;
const real gravity_eps = GM_EPS;
assert(gravity_eps > 0.0);
const real h = gravity_eps;
const real q = ds/h;
const real q2 = q*q;
const real q3 = q2*q;
const real q4 = q2*q2;
const real q5 = q3*q2;
real pot;
real acc;
if (q < 1)
{
acc = -1.0/sqr(h) * (4.0/3*q - 6.0/5*q3 + 0.5f*q4);
pot = +1.0/ h * (2.0/3*q2 - 0.3f *q4 + 0.1f*q5 - 7.0/5);
}
else if (q < 2)
{
acc = -1.0/sqr(h) * (8.0/3*q - 3.0*q2 + 6.0/5*q3 - 1.0/6*q4 - 1.0/15/q2);
pot = +1.0/ h * (4.0/3*q2 - q3 + 0.3*q4 - 1.0/30*q5 - 8.0/5 + 1.0/15/q);
}
else
{
acc = -ids2;
pot = -ids;
}
acc *= gravity_mass*ids;
pot *= gravity_mass;
return std::make_pair(acc * pos, pot);
}
const vec3 project(const vec3 &r, const vec3 &v)
{
return (v - r*((r*v)/r.norm2()));
}
