
SIP


The Strongly Implicit Procedure package is used to solve the finite difference equations in each step of a MODFLOW stress period.


•Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, M.G., 2000, MODFLOW2000, the U.S. Geological Survey modular groundwater model  User guide to modularization concepts and the GroundWater Flow Process: U.S. Geological Survey OpenFile Report 0092, 121 p.
•Harbaugh, A.W., 2005, MODFLOW2005, the U.S. Geological Survey modular groundwater model  the GroundWater Flow Process: U.S. Geological Survey Techniques and Methods 6A16. https://doi.org/10.3133/tm6A16 

Solvers


•MODFLOW2000
•MODFLOW2005
•MODFLOWLGR
•MODFLOWCFP
•MODFLOWNWT
•MODFLOWOWHM 

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

Input Instructions
Input to the Strongly Implicit Procedure (SIP) Package is read from the file that is type "SIP" in the name file. All numeric variables are free format if the option “FREE” is specified in the Basic Package input file; otherwise, all the variables have 10character fields.
FOR EACH SIMULATION

Data Set 0

[#Text]
Item 0 is optional—“#” must be in column 1. Item 0 can be repeated multiple times.
Text—is a character variable (199 characters) that starts in column 2. Any characters can be included in Text. The “#” character must be in column 1. Except for the name file, lines beginning with # are restricted to these first lines of the file. Text is printed when the file is read.


Data Set 1

MXITER NPARM
MXITER—is the maximum number of times through the iteration loop in one time step in an attempt to solve the system of finitedifference equations.

NPARM—is the number of iteration variables to be used. Five variables are generally sufficient.



Data Set 2

ACCL HCLOSE IPCALC WSEED IPRSIP
ACCL—is the acceleration variable. It must be greater than zero and is generally equal to one. If a zero is entered, it is changed to one.

HCLOSE—is the head change criterion for convergence. When the maximum absolute value of head change from all nodes during an iteration is less than or equal to HCLOSE, iteration stops.

IPCALC—is a flag indicating where the seed for calculating iteration variables will come from.
•0—the seed entered by the user will be used.
•1—the seed will be calculated at the start of the simulation from problem variables. 
WSEED—is the seed for calculating iteration variables. It is always read, but it is used only if IPCALC is equal to zero.

IPRSIP—is the printout interval for SIP. If IPRSIP is equal to zero, it is changed to 999. The maximum head change (positive or negative) is printed for each iteration of a time step whenever the time step is an even multiple of IPRSIP. This printout also occurs at the end of each time step regardless of the value of IPRSIP.


