flopy.modflow.mfgmg Module¶
mfgmg module. Contains the ModflowGmg class. Note that the user can access the ModflowGmg class as flopy.modflow.ModflowGmg.
Additional information for this MODFLOW package can be found at the Online MODFLOW Guide.

class
flopy.modflow.mfgmg.
ModflowGmg
(model, mxiter=50, iiter=30, iadamp=0, hclose=1e05, rclose=1e05, relax=1.0, ioutgmg=0, iunitmhc=None, ism=0, isc=0, damp=1.0, dup=0.75, dlow=0.01, chglimit=1.0, extension='gmg', unitnumber=None, filenames=None)¶ MODFLOW GMG Package Class.
Parameters: model : model object
The model object (of type
flopy.modflow.mf.Modflow
) to which this package will be added.mxiter : int
maximum number of outer iterations. (default is 50)
iiter : int
maximum number of inner iterations. (default is 30)
iadamp : int
is a flag that controls adaptive damping. The possible values of iadamp are.
If iadamp = 0, then the value assigned to DAMP is used as a constant damping parameter.
If iadamp = 1, the value of damp is used for the first nonlinear iteration. The damping parameter is adaptively varied on the basis of the head change, using Cooley’s method as described in Mehl and Hill (2001), for subsequent iterations.
If iadamp = 2, the relative reduced residual damping method documented in Mehl and Hill (2001) and modified by Banta (2006) is used.
When iadamp is specified as 2 and the value specified for DAMP is less than 0.5, the closure criterion for the inner iterations (drclose) is assigned simply as rclose. When damp is between 0.5 and 1.0, inclusive, or when iadamp is specified as 0 or 1, drclose is calculated according to equation 20 on p. 9 of Wilson and Naff (2004).
hclose : float
is the head change criterion for convergence. (default is 1e5).
rclose : float
is the residual criterion for convergence. (default is 1e5)
relax : float
is a relaxation parameter for the ILU preconditioned conjugate gradient method. The relax parameter can be used to improve the spectral condition number of the ILU preconditioned system. The value of relax should be approximately one. However, the relaxation parameter can cause the factorization to break down. If this happens, then the gmg solver will report an assembly error and a value smaller than one for relax should be tried. This item is read only if isc = 4.
ioutgmg : int
is a flag that controls the output of the gmg solver. The possible values of ioutgmg are.
If ioutgmg = 0, then only the solver inputs are printed.
If ioutgmg = 1, then for each linear solve, the number of pcg iterations, the value of the damping parameter, the l2norm of the residual, and the maxnorm of the head change and its location (column, row, layer) are printed. At the end of a time/stress period, the total number of gmg calls, pcg iterations, and a running total of pcg iterations for all time/stress periods are printed.
If ioutgmg = 2, then the convergence history of the pcg iteration is printed, showing the l2norm of the residual and the convergence factor for each iteration.
ioutgmg = 3 is the same as ioutgmg = 1 except output is sent to the terminal instead of the modflow list output file.
ioutgmg = 4 is the same as ioutgmg = 2 except output is sent to the terminal instead of the modflow list output file.
(default is 0)
iunitmhc : int
is a flag and a unit number, which controls output of maximum head change values. If iunitmhc = 0, maximum head change values are not written to an output file. If iunitmhc > 0, maximum head change values are written to unit iunitmhc. Unit iunitmhc should be listed in the Name file with ‘DATA’ as the file type. If iunitmhc < 0 or is not present, iunitmhc defaults to 0. (default is 0)
ism : int
is a flag that controls the type of smoother used in the multigrid preconditioner. If ism = 0, then ilu(0) smoothing is implemented in the multigrid preconditioner; this smoothing requires an additional ector on each multigrid level to store the pivots in the ilu factorization. If ism = 1, then symmetric gaussseidel (sgs) smoothing is implemented in the multigrid preconditioner. No additional storage is required if ism = 1; users may want to use this option if available memory is exceeded or nearly exceeded when using ism = 0. Using sgs smoothing is not as robust as ilu smoothing; additional iterations are likely to be required in reducing the residuals. In extreme cases, the solver may fail to converge as the residuals cannot be reduced sufficiently. (default is 0)
isc : int
is a flag that controls semicoarsening in the multigrid preconditioner. If isc = 0, then the rows, columns and layers are all coarsened. If isc = 1, then the rows and columns are coarsened, but the layers are not. If isc = 2, then the columns and layers are coarsened, but the rows are not. If isc = 3, then the rows and layers are coarsened, but the columns are not. If isc = 4, then there is no coarsening. Typically, the value of isc should be 0 or 1. In the case that there are large vertical variations in the hydraulic conductivities, then a value of 1 should be used. If no coarsening is implemented (isc = 4), then the gmg solver is comparable to the pcg2 ilu(0) solver described in Hill (1990) and uses the least amount of memory. (default is 0)
damp : float
is the value of the damping parameter. For linear problems, a value of 1.0 should be used. For nonlinear problems, a value less than 1.0 but greater than 0.0 may be necessary to achieve convergence. A typical value for nonlinear problems is 0.5. Damping also helps control the convergence criterion of the linear solve to alleviate excessive pcg iterations. (default 1.)
dup : float
is the maximum damping value that should be applied at any iteration when the solver is not oscillating; it is dimensionless. An appropriate value for dup will be problemdependent. For moderately nonlinear problems, reasonable values for dup would be in the range 0.5 to 1.0. For a highly nonlinear problem, a reasonable value for dup could be as small as 0.1. When the solver is oscillating, a damping value as large as 2.0 x DUP may be applied. (default is 0.75)
dlow : float
is the minimum damping value to be generated by the adaptivedamping procedure; it is dimensionless. An appropriate value for dlow will be problemdependent and will be smaller than the value specified for dup. For a highly nonlinear problem, an appropriate value for dlow might be as small as 0.001. Note that the value specified for the variable, chglimit, could result in application of a damping value smaller than dlow. (default is 0.01)
chglimit : float
is the maximum allowed head change at any cell between outer iterations; it has units of length. The effect of chglimit is to determine a damping value that, when applied to all elements of the headchange vector, will produce an absolute maximum head change equal to chglimit. (default is 1.0)
extension : list string
Filename extension (default is ‘gmg’)
unitnumber : int
File unit number (default is None).
filenames : str or list of str
Filenames to use for the package and the output files. If filenames=None the package name will be created using the model name and package extension and the gmg output name will be created using the model name and .cbc extension (for example, modflowtest.gmg.out), if iunitmhc is a number greater than zero. If a single string is passed the package will be set to the string and gmg output names will be created using the model name and .gmg.out extension, if iunitmhc is a number greater than zero. To define the names for all package files (input and output) the length of the list of strings should be 2. Default is None.
Returns: None
Examples
>>> import flopy >>> m = flopy.modflow.Modflow() >>> gmg = flopy.modflow.ModflowGmg(m)

static
load
(f, model, ext_unit_dict=None)¶ Load an existing package.
Parameters: f : filename or file handle
File to load.
model : model object
The model object (of type
flopy.modflow.mf.Modflow
) to which this package will be added.ext_unit_dict : dictionary, optional
If the arrays in the file are specified using EXTERNAL, or older style array control records, then f should be a file handle. In this case ext_unit_dict is required, which can be constructed using the function
flopy.utils.mfreadnam.parsenamefile
.Returns: gmg : ModflowGmg object
Examples
>>> import flopy >>> m = flopy.modflow.Modflow() >>> gmg = flopy.modflow.ModflowGmg.load('test.gmg', m)

write_file
()¶ Write the package file.
Returns: None

static