code: public void addCoords(Point3d[] iAtoms, Point3d[] jAtoms) {
  		addCoords(iAtoms, null, jAtoms, null);
  	}
docs: Adds the i and j coordinates and fills the grid. Their bounds will be computed.
  Subsequent call to {@link #getIndicesContacts()} will produce the
  contacts, i.e. the set of points within distance cutoff.
  
  Subsequent calls to method {@link #getAtomContacts()} will produce a NullPointerException
  since this only adds coordinates and no atom information.
  @param iAtoms
  @param jAtoms