public static Cell makeCell ()
{
Cell c = new Cell ();
c.initNode ();
c.subp = new Node[NSUB];
for (int i = 0; i < Cell.NSUB; ++i)
c.subp [i] = null;
return c;
}
/**
* Initialize the tree structure for hack force calculation.
*
* @param nsteps the current time step
*/
private void makeTree (int nstep)
{
Body q0 = this.bodyTabRev [0];
q0.expandBox (this, nstep);
Body q1 = this.bodyTabRev [1];
q1.expandBox (this, nstep);
MathVector xqicinit = intcoord (q1.pos);
this.root = q0.loadTree (q1, xqicinit, Node.IMAX >> 1, this);
for (int i = 2; i < this.bodyTabRev.Count; ++i) {
Body q = this.bodyTabRev [i];
if (q.mass != 0.0) {
q.expandBox (this, nstep);
MathVector xqic = intcoord (q.pos);
root = root.loadTree (q, xqic, Node.IMAX >> 1, this);
}
}
root.hackcofm ();
}
/**
* Advance the N-body system one time-step.
*
* @param nstep the current time step
*/
public void stepSystem (int nstep)
{
// free the tree
root = null;
makeTree (nstep);
// compute the gravity for all the particles
for (int i = 0; i < this.bodyTabRev.Count; ++i)
this.bodyTabRev [i].hackGravity (rsize, root);
vp (bodyTabRev, nstep);
}