Since GeoDict 2023, two solvers are available for the Effective Stiffness calculation: FeelMath and LIR. The FeelMath solver is developed at Fraunhofer ITWM since over a decade. It is more versatile, has more features and is currently recommended for most use cases. The LIR solver is developed in-house at Math2Market and is already known and refined from other modules, like e.g. FlowDict. For effective stiffness calculations, it has a low memory consumption on highly porous structures, and it is fast with symmetric boundary conditions.

Internally, both solvers solve several equations for strain and stress at each voxel by using iterative solvers. The basic idea of an iterative method is to:

1. Start with some initial guess for the unknown values.
2. Improve the current values in each iterative step. The improvement can be fast or extremely slow depending on the parameters.
3. Repeat the iterative process until the stopping criteria is fulfilled.

The parameters for FeelMath and LIR differ and are explained in the following two sections.