1. * USTHB, Faculty of Mathematics , RECIT Laboratory , Po. Box 32, El Alia, 16111 , Algiers , ALGERIA
2. CERIST: Research Center for Scientific and Technical Information , 05 Rue des trois fréres Aissou, Ben Aknoun , Algiers , ALGERIA , belbachir@cerist.dz
3. ** Faculty of Sciences , Oran1 University , GEAN Laboratory , Po. Box 1524, El Menaouer, 31000 Es Senia , Oran , ALGERIA
4. *** Faculty of Sciences , Oran1 University , GEAN Laboratory , Po. Box 1524, El Menaouer, 31000 Es Senia , Oran , ALGERIA
5. USTHB, Faculty of Mathematics , RECIT Laboratory , Po. Box 32, El Alia, 16111 Algiers , ALGERIA