add nodal_factors function

Author: qiangshu

vtools/__init__.py

@@ -39,4 +39,5 @@
 from vtools.functions.lag_cross_correlation import *
 from vtools.functions.envelope import *
 from vtools.functions.neighbor_fill import fill_from_neighbor,dfm_pack_params,save_dfm_params,load_dfm_params
-from vtools.functions.coarsen import ts_coarsen 
+from vtools.functions.coarsen import ts_coarsen 
+from vtools.functions.ha_utils import nodal_factors