# GMS:MF6 IMS Package

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MODFLOW 6 is currently in Beta release for GMSSome features and capabilities of MODFLOW 6 are still in development for GMS. |

MODFLOW 6 | |
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Models & Tools | |

GWF Model GWT Model Cell Properties Dialog Zone File | |

Packages | |

Flow: |
GNC, HFB, NPF |

GWF: |
BUY, CHD, CSUB, DRN, EVT, GHB, LAK, MAW, MVR, OBS, RCH,RIV, SFR, STO, UZF, WEL |

GWT: |
ADV, CNC, DSP FMI, IC, IST, LKT, MDT, MST, MVT, MWT, OBS, SFT, SRC,SSM, UZT |

Other |
DIS, DISU, DISV, IMS, OC, TDIS, PEST |

The *Iterative Model Solution (IMS)* dialog is accessed by double-clicking on the IMS package under a MODFLOW 6 simulation in the Project Explorer. It contains the following sections and options:

*Sections*list – A list of sections that can be turned on or off:*Comments*– Turn on to make the*Comments*section visible.*Options*– Turn on to make the*Options*section visible.*Nonlinear*– Turn on to make the*Nonlinear*section visible. This section is on by default.*Linear*– Turn on to make the*Linear*section visible. This section is on by default.

*Comments*section – Enter general alphanumeric comments. Comments entered here get written at the top of the file, preceded by a '#' symbol.*Options*section*PRINT_OPTION*– A flag that controls printing of convergence information from the solver. Turn on to make the following print options available from the drop-down:- "None" – Print nothing. This is the default when
*PRINT_OPTION*is not turned on. - "Summary" – Print only the total number of iterations and nonlinear residual reduction summaries
- "All" – Print linear matrix solver convergence information to the solution listing file and model specific linear matrix solver convergence information to each model listing file in addition to "Summary" information.

- "None" – Print nothing. This is the default when
*COMPLEXITY*– Optional. Defines default non-linear and linear solver parameters. Turn on to make the following options available from the drop-down:- "Simple" – Default solver input values will be defined that work well for nearly linear models.
- "Moderate" – Default solver input values will be defined that work well for moderately nonlinear models.
- "Complex" – Default solver input values will be defined that work well for highly nonlinear models.
**Set NONLINEAR and LINEAR Parameters to Complexity Defaults**– This will set all nonlinear and linear parameters to their default values corresponding to the current complexity setting. A confirmation dialog will appear.

*CSV_OUTER_OUTPUT FILEOUT*– Turn on to specify that the record corresponds to the comma separated values solver convergence output. Enter the desired filename for the output ASCII CSV file in the empty field to the right of the option.*CSV_INNER_OUTPUT FILEOUT*– Turn on to specify that the record corresponds to the comma separated values solver convergence output. Enter the desired filename for the output ASCII CSV file in the empty field to the right of the option.*NO_PTC*– Turn on to disable pseudo-transient continuation (PTC). Only applies to steady-state stress periods for models using the Newton-Raphson formulation.- "ALL"
- "FIRST"

*Nonlinear*section – A table with three columns: "Use" to turn on or off options, "Option" (giving the name of the option), and "Value", where a value can be entered for the option. The options include the following:*OUTER_DVCLOSE*– Real value defining the head change criterion for convergence of the outer (nonlinear) iterations, in units of length. Default value is "0.001".*OUTER_MAXIMUM*– Integer value defining the maximum number of outer (nonlinear) iterations. Default value is "25".*UNDER_RELAXATION*– Optional drop-down value. Defines the nonlinear under-relaxation schemes used.- "None" – Under-relaxation is not used.
- "Simple" – Simple under-relaxation scheme with a fixed relaxation factor is used.
- "Cooley" – Cooley under-relaxation scheme is used.
- "DBD" – Delta-bar-delta under-relaxation is used.

*UNDER_RELAXATION_THETA*– Real value defining the reduction factor for the learning rate (under-relaxation term) of the delta-bar-delta algorithm. Default value is "0.0".*UNDER_RELAXATION_KAPPA*– Real value defining the increment for the learning rate (under-relaxationterm) of the delta-bar-delta algorithm. Default value is "0.0".*UNDER_RELAXATION_GAMMA*– Real value defining the history or memory term factor of the delta-bar-delta algorithm. Default value is "0.0".*UNDER_RELAXATION_MOMENTUM*– Real value defining the fraction of past history changes that is added as a momentum term to the step change for a nonlinear iteration. Default value is "0.0".*BACKTRACKING_NUMBER*– Integer value defining the maximum number of backtracking iterations allowed for residual reduction computations. Default value is "0".*BACKTRACKING_TOLERANCE*– Only available if*BACKTRACKING_NUMBER" has a value of "1" or higher. Real value defining the tolerance for residual change that is allowed for residual reduction computations**BACKTRACKING_REDUCTION_FACTOR*– Only available if*BACKTRACKING_NUMBER" has a value of "1" or higher. Real value defining the reduction in step size used for residual reduction computations**BACKTRACKING_RESIDUAL_LIMIT*– Only available if*BACKTRACKING_NUMBER" has a value of "1" or higher. Real value defining the limit to which the residual is reduced with backtracking.**LINEAR_SOLVER*– Enter the linear solver being used.

*Linear*section – A table with three columns: "Use" to turn on or off options, "Option" (giving the name of the option) and "Value", where a value can be entered for the option. The options include the following:*INNER_MAXIMUM*– Integer value defining the maximum number of inner (linear) iterations. Default value of "50".*INNER_DVCLOSE (length)*– Real value defining the head change criterion for convergence of the inner (linear) iterations, in units of length. Default value of "0.001".*INNER_RCLOSE (length*– Real value that defines the flow residual tolerance for convergence of the IMS linear solver and specific flow residual criteria used. Default value of "0.1".^{3}/time)*RCLOSE_OPTION*– Optional. Defines the specific flow residual criterion used. Default selection of "None". Has the following options:- "None" – If selected, an absolute residual (infinity-norm) criterion is used.
- "Strict" – Specifies that INNERRCLOSE represents an infinity-Norm (absolute convergence criteria) and that the head and flow convergence criteria must be met on the first inner iteration.
- "L2NORM_RCLOSE" – Specifies that INNERRCLOSE represents a L-2 Norm closure criteria instead of an infinity-Norm (absolute con-vergence criteria).
- "RELATIVE_RCLOSE" – Spcifies that INNERRCLOSE represents a relative L-2 Norm reduction closure criteria instead of an infinity-Norm (absolute convergence criteria).

*LINEAR_ACCELERATION*– Defines the linear acceleration method used by the default IMS linear solvers. Default selection of "CG". Has the following options:- "CG" – Preconditioned conjugate gradient method.
- "BICGSTAB" – Preconditionedbi-conjugate gradient stabilized method.

*RELAXATION_FACTOR*– Optional. Real value that defines the relaxation factor used by the incomplete LU factorization preconditioners (MILU(0) and MILUT). Default value of "0.0".*PRECONDITIONER_LEVELS*– Optional. Integer value defining the level of fill for ILU decomposition used in the ILUT and MILUT preconditioners. Default value of "0".*PRECONDITIONER_DROP_TOLERANCE*– Optional. Real value that defines the drop tolerance used to drop preconditioner terms based on the magnitude of matrix entries in the ILUT and MILUT preconditioners. Default value of "0.0".*NUMBER_ORTHOGONALIZATIONS*– Optional. Integer value defining the interval used to explicitly recalculate the residual of the flow equation using the solver coefficient matrix, the latest head estimates, and the right hand side. Default value of "0".*SCALING_METHOD*– Optional. Defines the matrix scaling approach used. Default selection of "None". Has the following options:- "None" – No matrix scaling applied.
- "Diagonal" – Symmetric matrix scaling using the POLCG preconditioner scaling method.
- "L2NORM" – Symmetric matrix scaling using the L2 norm.

*REORDERING_METHOD*– Optional. Defines the matrix reordering approach used. Default selection of "None". Has the following options:- "None" – Original ordering.
- "RCM" – Reverse Cuthill McKee ordering.
- "MD" – Minimum degree ordering.

## Related Topics

GMS – Groundwater Modeling System | ||
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Modules: | 2D Grid • 2D Mesh • 2D Scatter Point • 3D Grid • 3D Mesh • 3D Scatter Point • Boreholes • GIS • Map • Solid • TINs • UGrids | |

Models: | FEFLOW • FEMWATER • HydroGeoSphere • MODAEM • MODFLOW • MODPATH • mod-PATH3DU • MT3DMS • MT3D-USGS • PEST • PHT3D • RT3D • SEAM3D • SEAWAT • SEEP2D • T-PROGS • ZONEBUDGET | |

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