public final void hackGravity(double rsize,Node root){
  MathVector pos0=(MathVector)pos.clone();
  HG hg=new HG(this,pos);
  hg=root.walkSubTree(rsize * rsize,hg);
  phi=hg.phi0;
  newAcc=hg.acc0;
}

public final void hackGravity ( double rsize , Node root ) { MathVector pos0 = ( MathVector ) pos . clone ( ) ; HG hg = new HG ( this , pos ) ; hg = root . walkSubTree ( rsize * rsize , hg ) ; phi = hg . phi0 ; newAcc = hg . acc0 ; }
evaluate gravitational field on the body . the original olden version calls a routine named " walkscan " , but we use the same name that is in the barnes code .
