Balanced incomplete factorization preconditioner with pivoting

In this work we study pivoting strategies for the preconditioner presented in Bru (SIAM J Sci Comput 30(5):2302–2318, 2008) which computes the LU factorization of a matrix A . This preconditioner is based on the Inverse Sherman Morrison (ISM) decomposition [Preconditioning sparse nonsymmetric linear systems with the Sherman–Morrison formula. Bru (SIAM J Sci Comput 25(2):701–715, 2003), that using recursion formulas derived from the Sherman-Morrison formula, obtains the direct and inverse LU factors of a matrix. We present a modification of the ISM decomposition that allows for pivoting, and so the computation of preconditioners for any nonsingular matrix. While the ISM algorithm at a given step computes only a new pair of vectors, the new pivoting algorithm in the k -th step also modifies all the remaining vectors from k + 1 to n . Thus, it can be seen as a right looking version of the ISM decomposition. The results of numerical experiments with ill-conditioned and highly indefinite matrices arising from different applications show the robustness of the new algorithm, since it is able to solve problems that are not possible to solve otherwise.