Solution settings

Solution settings control how the step is solved: which linear solver is used, how many iterations are allowed, and when the solution counts as converged.

The defaults are chosen to work for most models. This is the branch to open when a step fails to converge, not one to adjust routinely.

Solver settings

Setting	Default	Meaning
Linear solver	Pardiso	The linear equation solver — Pardiso, Simple, Mumps or diagonal
Extrapolation	default	How the next increment is predicted — default, linear, quadratic, coupled, constant or none
Maximum number of increments	1e4	Upper limit on increments in the step
Maximum number of iterations	32	Iterations allowed per increment before a cutback
Minimum number of iterations	1	Iterations performed before convergence is tested
No cutback	No	When Yes, the time step is never reduced after a failed increment

If an increment does not converge within the maximum number of iterations, the time step is cut back and the increment retried. Setting No cutback to Yes removes that safety net, so the calculation stops instead of retrying.

Controls

Convergence is tested separately for each solution variable. Two control groups are available: Displacement and Pore water pressure.

Each has a Status:

Status	Effect
Default	The built-in tolerances are used
Modify	The tolerances below become editable
Deactivate	This variable is not tested for convergence

With Modify selected, six values appear:

Value	Default	Meaning
Tol. Solution	1e-2	Tolerance on the solution increment
Tol. Energy	1e-2	Tolerance on the energy
Tol. Force	1e-2	Tolerance on the residual force
Zero Solution Inc.	1e-6	Below this, the solution increment counts as zero
Zero Energy Inc.	1e-6	Below this, the energy increment counts as zero
Relaxation Factor	2	Relaxation applied to this variable

Warning

Deactivating a control stops that variable being checked at all. An increment can then be accepted while the pore pressure is still far from equilibrium. Loosening a tolerance is usually the better response to a stubborn step.

The pore water pressure controls apply to two- and three-phase analyses. In a single-phase analysis there is no pore pressure to test.

Accelerators

An accelerator adjusts the iteration to reach convergence in fewer steps.

Method	Parameters
Default	—
Relaxation	λ (default 0.8)
Back-looking	λmin (0.5), λmax (1.0)
Linear	λmin (0.5), λmax (1.0)
Anderson	αmax (2.0), depth (1.0)

Only the parameters of the selected method are shown.

Solver and control settings are described under Solver and Controls in the numgeo reference manual.