ldouble yAcceleration(Particle p, vector<Particle> particles) {
ldouble acceleration = 0;
for(auto i = particles.begin(); i != particles.end(); ++i) {
ldouble dy = p.py - i->py;
if(fabs(dy) > numeric_limits<ldouble>::epsilon())
acceleration += i->mass / dy*dy * -signum(dy);
}
return acceleration * GRAVITY;
}
ldouble xAcceleration(Particle p, vector<Particle> particles) {
ldouble acceleration = 0;
for(auto i = particles.begin(); i != particles.end(); ++i) {
ldouble dx = p.px - i->px;
if(fabs(dx) > numeric_limits<ldouble>::epsilon())
acceleration += i->mass / dx*dx * -signum(dx);
}
return acceleration * GRAVITY;
}