public Point3f getCenterOfSelectedAtoms(BitSet bs) {
		Point3f p = new Point3f();
		if (iAtom <= 0 || bs.cardinality() <= 0)
			return p;
		int n = 0;
		for (int i = 0; i < iAtom; i++) {
			if (bs.get(i)) {
				p.x += atom[i].rx;
				p.y += atom[i].ry;
				p.z += atom[i].rz;
				n++;
			}
		}
		float inverse = 1.0f / n;
		p.x *= inverse;
		p.y *= inverse;
		p.z *= inverse;
		return p;
	}