Hakopian, Y. and Hovhannisyan, R. (2014) “ON THE TWO-LEVEL PRECONDITIONING IN LEAST SQUARES METHOD”, Proceedings of the YSU A: Physical and Mathematical Sciences. Yerevan, Armenia, 48(1 (233), pp. 7–15. doi: 10.46991/PSYU:A/2014.48.1.007.