n-body halving example

gistfile1.java

class CelestialBody {

  double mass;
  QVector3D position;
  QVector3D velocity;

  QVector3D f[];

}

// …
for (int i = 0; i < bodies.length; i++) {
  for (int j = 0; j < bodies[i].f.length; j++) {
    bodies[i].f[j] = new QVector3D(0, 0, 0);
  }
}

CelestialBody[] bodies;
for (int i = 0; i < bodies.length; i++) {
  CelestialBody current = bodies[i];
  double mu = G * current.mass;
  for (int j = i + 1; j < bodies.length; j++) {
    CelestialBody body = bodies[j];
    QVector3D direction = body.position[r] - current.position[r];
    double distanceSquared = direction.lengthSquared();
    QVector3D f = (mu * body.mass / distanceSquared) * direction.normalized();
    current.f[threadIndex] += f;
    body.f[threadIndex] -= f;
  }
}

for (int i = 0; i < bodies.length; i++) {
  CelestialBody current = bodies[i];
  QVector3D f = new QVector3D(0, 0, 0);
  for (int j = 0; j < current.f.length; j++) {
    f += current.f[j];
  }
  QVector3D a = f / current.mass;
  current.velocity[w] = current.velocity[r] + (a * time);
  current.position[w] = current.position[r] + (current.velocity[w] * time);
}