User's guide of Proceessing Modflow 5.0

Processing Modflow 105
< Allowed Iteration Numbers: MXITER is the maximum number of outer iterations. For
each outer iteration, A_ and b_ (eq. 3.30) are updated by using the newly calculated hydraulic
heads. For a linear problem, MXITER should be 1, unless more that 50 inner iterations are
required. A larger number (generally less than 100) is required for a nonlinear problem.
Outer interations continue until the final convergence criteria (see below) are met on the first
inner iteration. ITER1 is the maximum number of inner iterations. Eq. 3.30 with a new set
of A_ and b_ is solved in inner iterations. The inner iterations continue until ITER1- iterations
are executed or the final convergence criteria (see below) are met.
< Convergence Criteria: Head Change [L] is the head change criterion for convergence.
When the maximum absolute value of the head change at all nodes during an iteration is less
than or equal to the specified Head Change, and the criterion for Residual is satisfied (see
3 -1
below), iteration stops. Residual [L T ] is the residual criterion for convergence. Residual
is calcuated as b_ - A_ · x_ for each inner iteration. When the maximum absolute value of the
residual at all cells during an iteration is less than or equal to Residual, and the criterion for
Head Change is satisfied (see above), iteration stops.
< Printout From the Solver: A positive integer is required by Printout Interval. If the option
All available information is selected, the maximum head change and residual (positive or
negative) are saved in the run record file OUTPUT.DAT for each iteration of a time step
whenever the time step is an even multiple of Printout Interval. If the option The number
of iterations only is checked, the printout of maximum head change and residual is
suppressed. Select the option None to suppress all printout from the solver.
Fig. 3.30 The Preconditioned Conjugate Gradient Package 2 dialog box
3.6.1 MODFLOW