\documentstyle[12pt]{article} \textwidth 6.4in \textheight 8.8in \topmargin 0in \headsep 0in \oddsidemargin 0in \evensidemargin 0in \newtheorem{th}{Theorem}[section] \newtheorem{lem}{Lemma}[section] \newtheorem{de}{Definition}[section] \newtheorem{al}{Algorithm}[section] \newcommand{\To}{\Rightarrow} \newcommand{\R}{I\!\!R} \newcommand{\be}{\begin{equation}} \newcommand{\ee}{\end{equation}} \newcommand{\proof}{\rm {\bf P\,r\,o\,o\,f.}} \newcommand{\proofend}{\diamondsuit} \date{} \thispagestyle{empty} \title {Efficient Monte Carlo Algorithms for Inverting Matrices Arising in Mixed Finite Element Approximation} \author {T.T. Dimov $^{1}$} \begin{document} \maketitle \footnotetext[1]{ Central Laboratory for Parallel Processing, Department of Parallel Algorithms, Bulgarian Academy of Sciences, Acad. G. Bonchev St.,bl. 25 A, \,\, 1113 \,\, Sofia, Bulgaria, e-mail: tdimov@iscbg.acad.bg, \, Web site: http://www.acad.bg/BulRTD/math/dimov2.html} \begin{abstract} A new approach for inverting matrices arising after Raviart-Thomas mixed finite element discretization of second-order elliptic equations is studied. Two Monte Carlo algorithms are considered. The first algorithm is based on a special techniques, which uses different relaxation parameters in the iterative procedure and improves the inverse matrix approximation column by column. The second algorithm derives a good error balancing for these special matrices row by row. All parameters determining the efficiency of the algorithms are controled automatically by a posteriori criteria based on some essential properties of the residual matrices. Numerical computations for rectangular finite elements are presented. The algorithms under consideration are well parallelized. \end{abstract} {\it Keywords:} Monte Carlo algorithms, mixed finite element method, iterative methods, Markov chain, inverse matrix problem. {\it ASM subject classifications:} 65C05, 65U05, 65F10, 65Y20. \end{document}