1. J.H. Adler, P.S. Vassilevski, Error analysis for constrained first-order system least-squares finite-element methods. SIAM J. Sci. Comput. 36 (3), A1071–A1088 (2014)
2. Z. Cai, R. Lazarov, T.A. Manteuffel, S.F. McCormick, First-order system least squares for second-order partial differential equations. I. SIAM J. Numer. Anal. 31 (6), 1785–1799 (1994)
3. G.F. Carey, A.I. Pehlivanov, P.S. Vassilevski, Least-squares mixed finite element methods for non-selfadjoint elliptic problems. II. Performance of block-ILU factorization methods. SIAM J. Sci. Comput. 16(5), 1126–1136 (1995)
4. M. Christensen, U. Villa, P.S. Vassilevski, Multilevel techniques lead to accurate numerical Upscaling and Scalable Robust Solvers for Reservoir Simulation, in SPE Reservoir Simulation Symposium, 23–25 February, Houston, Texas, USA, SPE-173257-MS, 2015
5. HYPRE, A library of high performance preconditioners, http://www.llnl.gov/CASC/hypre/