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Navigation: Online Guide to MODFLOW > Groundwater Flow Process > Solvers

GMG - Geometric Multigrid Solver

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Abbreviation in Name file

GMG

Purpose

The Geometric Multigrid Solver is used to solve the finite difference equations in each step of a MODFLOW stress period.

Documentation

Wilson, J.D. and Naff, R.L., 2004, The U.S. Geological Survey modular ground-water model -- GMG linear equation solver package documentation: U.S. Geological Survey Open-File Report 2004-1261, 47 p.

Banta, Edward R., 2006, Modifications to MODFLOW boundary conditions and an adaptive-damping scheme for Picard iterations for a highly nonlinear regional model, in Poeter, Eileen, Hill, Mary, and Zheng, Chunmiao, MODFLOW and More 2006—Managing Ground Water Systems: International Ground Water Modeling Center and Colorado School of Mines, Golden, Colorado, 2006 [Proceedings], p. 596-600.

GMG_Damping.pdf

Related Packages

Solvers

Supported in

MODFLOW-2000

MODFLOW-2005

MODFLOW-LGR

MF2005-NWT

MODFLOW-OWHM

Other Notes

If the Lake package is used, more iterations may be required.

Input Instructions

The GMG solver package has both an inner loop and outer loop. The inner loop is set up for the convergence of the linear problem and is controlled by the parameters RCLOSE and IITER. A nonlinear problem is controlled through the outer loop and uses parameters HCLOSE and MXITER. As a solution of the linear problem is used as an approximate solve for the nonlinear problem, all four parameters are needed when solving a nonlinear problem. The operation of these parameters is further explained in the section titled “Module GMG1AP”.

Input for the GMG package is read from the file that is type ”GMG” in the name file. Free format is used for reading all values on the input list. The GMG data file should contain the following data items:

FOR EACH SIMULATION

Data Set -1

[#Text]

Item -1 is optional—“#” must be in column 1. Item 0 can be repeated multiple times.

Data Set 0

RCLOSE IITER HCLOSE MXITER

Data Set 1

DAMP IADAMP IOUTGMG [IUNITMHC]

Data Set 2

ISM ISC [DUP DLOW CHGLIMIT]

DUP, DLOW, and CHGLIMIT are only read if IADAMP = 2.

Data Set 3

RELAX

This item is read only if ISC = 4