GCG: Generalized Conjugate Gradient Solver Pane

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The GCG: Generalized Conjugate Gradient Solver pane is is on the MODFLOW Packages and Programs dialog box under MT3DMS or MT3D-USGS. It is used to specify some of the data for the GCG solver in MT3DMS. The GCG solver is required for all MT3DMS models.

hmtoggle_plus1MXITER

MXITER is the maximum number of outer iterations; it should be set to an integer greater than one only when a nonlinear sorption isotherm is included in simulation.
hmtoggle_plus1ITER1

ITER1 is the maximum number of inner iterations; a value of 30-50 should be adequate for most problems.
hmtoggle_plus1ISOLVE

ISOLVE is the type of preconditioners to be used with the Lanczos/ORTHOMIN acceleration scheme:

= 1, Jacobi

= 2, SSOR

= 3, Modified Incomplete Cholesky (MIC) (MIC usually converges faster, but it needs significantly more memory)
hmtoggle_plus1NCRS

NCRS is an integer flag for treatment of dispersion tensor cross terms:

= 0, lump all dispersion cross terms to the right-hand-side (approximate but highly efficient).

= 1, include full dispersion
hmtoggle_plus1ACCL

ACCL is the relaxation factor for the SSOR option; a value of 1.0 is generally adequate.
hmtoggle_plus1CCLOSE

CCLOSE is the convergence criterion in terms of relative concentration; a real value between 10-4 and 10-6 is generally adequate.
hmtoggle_plus1IPRGCG

IPRGCG is the interval for printing the maximum concentration changes of each iteration. Set IPRGCG to zero as default for printing at the end of each stress period.