>>> CONSECUTIVE: max_iter1
By default, TOUGH2 simulations are stopped if 10 consecutive time steps converge with a single Newton-Raphson iteration because no update of primary variables occurs. This command allows changing the maximum number of allowable time steps with ITER=1 to max_iter1. Consecutive time steps with no update of primary variable occur if:
(1) steady-state is reached;
(2) calibration or printout times are too narrowly spaced;
(3) the maximum time step size (TOUGH2 variable DELTMX) is too small;
(4) the initial time step (TOUGH2 variable DELTEN or DLT(1)) is too small;
(5) a small time step is taken to land on a calibration or printout time.
Only (1) is an acceptable TOUGH2 convergence (see command >>> STEADY-STATE). All the other reasons may lead to premature termination of a TOUGH2 simulation. Convergence problems are more often encountered in iTOUGH2 than in a standard TOUGH2 simulation because many parameter combinations are submitted. This command makes TOUGH2 more tolerant of this kind of convergence failure. It is important, however, that max_iter1 is only increased to overcome temporary convergence problems during the optimization, i.e., the final parameter set should yield a TOUGH2 simulation without convergence problems. Calibration points should not be spaced too narrowly in time (see command >> TIME). Command >>> ADJUST can be used to overcome problem (4). Note that a special time stepping procedure is incorporated in iTOUGH2 to avoid problem (5).
>>> accept : 20 CONSECUTIVE time steps that converge on ITER=1