  A symmetric and a nonsymmetric variant of the additive Schwarz preconditioner
are proposed for the solution of a nonsymmetric system of algebraic equations
arising from a general finite volume element discretization of symmetric
elliptic problems with large jumps in the entries of the coefficient matrices
across subdomains. It is shown in the analysis, that the convergence of the
preconditioned GMRES iteration with the proposed preconditioners, depends
polylogarithmically on the mesh parameters, in other words, the convergence is
only weakly dependent on the mesh parameters, and it is robust with respect to
the jumps in the coefficients.
