# Grid Solver#

## What is the grid solver?#

Actually, DAMASK contains three different grid solvers that are invoked with **DAMASK_grid**:
Two Fast Fourier Transform (FFT)-based spectral solvers and one FEM solver.
Which out of these three alternatives (`spectral_basic`

, `spectral_polarization`

, or `FEM`

) is used in the calculation can be specified with the `solver:mechanical`

key in the loadcase file.
All three grid solvers operate on hexahedral volume elements discretized by a regular grid that is subjected to periodic boundary conditions.
See Grid Solver/Load Case for more details.

## Can I use the grid solver for non-periodic situations?#

Not directly. Nevertheless, it is possible to break periodicity in certain directions by using a suitable constitutive model. A layer of soft dilatational material would, for example, result in (almost) zero stress conditions. Still, the mesh solver or MSC.Marc are usually better options for non-periodic boundary conditions.