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