The options that are required if Options is set to "Specified" and LINMETH is set to GMRES are on the GMRES Variables of the NWT: Newton Solver pane of the the MODFLOW Packages and Programs dialog box under Solvers.
MAXITINNER is the maximum number of iterations for the linear solution (integer).
ILUMETHOD is the index for selection of the method for incomplete factorization (ILU) used as a preconditioner. See Kipp and others (2008) for further details (integer).
•ILUMETHOD=1—ILU with drop tolerance and fill limit. Fill-in terms less than drop tolerance times the diagonal are discarded. The number of fill-in terms in each row of L and U is limited to the fill limit. The fill-limit largest elements are kept in the L and U factors.
•ILUMETHOD=2 — ILU(k), Order k incomplete LU factorization. Fill-in terms of higher order than k in the factorization are discarded.
LEVFILL is the fill limit for ILUMETHOD = 1 and is the level of fill for ILUMETHOD = 2. Recommended values: 5-10 for method 1, 0-2 for method 2. See Kipp and others (2008) for further details.
STOPTOL is the tolerance for convergence of the linear solver. This is the residual of the linear equations scaled by the norm of the root mean squared error. Usually 10-8 to 10-12 works well. See Kipp and others (2008) for further details.
MSDR is the number of iterations between restarts of the GMRES Solver. See Kipp and others (2008) for further details (integer).
