Solver Options 2

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The Solver Options 2 pane is on the SWR: Surface-Water Routing Process Pane of the MODFLOW Packages and Programs dialog box.

The Solver Options 2 pane is used to specify additional parameters related to solving the surface-water flow equations.

Preconditioner (IPC): IPC defines the preconditioner with the iterative solver used by the SWR1 Process to solve the defined surface-water equations for each reach group. IPC is only defined if ISOLVER > 1.

Maximum number of levels (NLEVELS): NLEVELS defines the maximum number of levels to use for each row of U and each row of L. NLEVELS values between 5 and 10 have been found to work well for the test problems evaluated. NLEVELS is only specified if IPC = 4.

Drop threshold (DROPTOL): DROPTOL defines the threshold for dropping small terms in the factorization. A DROPTOL value of 1×10-3 has been found to work well for the test problems evaluated. DROPTOL is only specified if IPC = 4.

Interval for printing line search information (IBTPRT): IBTPRT is a flag for writing a summary of line-search information to the MODFLOW listing file for each SWR1 outer iteration when line search is attempted. Line-search information summarized includes the SWR1 outer iteration number, number of line search iterations, initial ℓ2-norm of the residual, final ℓ2-norm of the residual, final relaxation parameter value (λ), and whether the estimated stage was updated at the end of the line search routine. If IBTPRT > 0, then summary line-search data are written to the MODFLOW listing file every IBTPRT SWR1 outer iteration when line search is attempted. IBTPRT is only specified if IBT > 1.

Alternative flow tolerance (PTOLR): PTOLR defines the alternative tolerance level for reach group flow residuals to evaluate convergence for flow within the selected numerical solver and to trigger increases and decreases in the SWR1 time steps when adaptive time stepping is enabled. PTOLR is only specified if USE_FRACTIONAL_TOLR or USE_L2NORM_TOLR is specified. If USE_L2NORM_TOLR is specified, value is in units of length cubed per time, and must be consistent with MODFLOW length and time units. Otherwise, the PTOLR value is unitless.