SIP: Strongly Implicit Procedure Package

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The Strongly Implicit Procedure (SIP) package is another solver commonly used in MODFLOW models. The pane for this package is on the MODFLOW Packages and Programs dialog box under Solvers.

The following items are set on the SIP: Strongly Implicit Procedure Package pane.

Max. number of iterations (MXITER) is the maximum number of times through the iteration loop in one time step in an attempt to solve the system of finite-difference equations. If the Lake package is used, more iterations may be required.

Number of iteration variables (NPARM) is the number of iteration variables to be used. Five variables are generally sufficient.

Acceleration variable (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.

Head change criterion (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.

Seed source (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.

Seed for seed for calculating iteration variables (WSEED) is the seed for calculating iteration variables. It is always read, but it is used only if IPCALC is equal to zero.

Printout interval (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.