Hakopian, Yu.A., and R.Z. Hovhannisyan. “ON THE TWO-LEVEL PRECONDITIONING IN LEAST SQUARES METHOD”. Proceedings of the YSU A: Physical and Mathematical Sciences 48, no. 1 (233) (April 10, 2014): 7–15. Accessed July 22, 2024. https://journals.ysu.am/index.php/proceedings-phys-math/article/view/vol48_no1_2014_pp007-015.