AIP Conference Proceedings [AIP APPLICATION OF MATHEMATICS IN TECHNICAL AND NATURAL SCIENCES: 4th International Conference--AMiTaNS '12 Memorial Volume devoted to Prof. Christo I. Christov - St. Constantine and Helena, Bulgaria (11–16 June 2012)] - Numerical experiments with applying approximate LU-factorizations as preconditioners for solving SLAEs with coefficient matrices from the "Sparse Matrix Market"