# Categories of parameters#

The parameters that can be provided in the input file can roughly be categorized into the following groups:

Global parameters (see Global parameters): These parameters determine the overall behavior of the program. Primarily they describe things like the output directory, the end time of the simulation, or whether the computation should be resumed from a previously saved state.

Parameters for certain aspects of the numerical algorithm: These describe, for example, the specifics of the spatial discretization. In particular, this is the case for parameters concerning the polynomial degree of the finite element approximation (Discretization), some details about the stabilization (Subsection: Discretization / Stabilization parameters), and how adaptive mesh refinement is supposed to work (Mesh refinement).

Parameters that describe certain global aspects of the equations to be solved: This includes, for example, a description if certain terms in the model should be omitted or not. See Formulation for the list of parameters in this category.

Parameters that characterize plugins: Certain behaviors of ASPECT are described by what we call

*plugins*- self-contained parts of the code that describe one particular aspect of the simulation. An example would be which of the implemented material models to use, and the specifics of this material model. The sample parameter file above gives an indication of how this works: within a subsection of the file that pertains to the material models, one can select one out of several plugins (or, in the case of the postprocessors, any number, including none, of the available plugins), and one can then specify the specifics of this model in a sub-subsection dedicated to this particular model.A number of components of ASPECT are implemented via plugins. Some of these, together with the sections in which their parameters are declared, are the following:

The material model: Sections Material model and following.

The geometry: Sections Geometry model and following.

The gravity description: Sections Gravity model and following.

Initial conditions for the temperature: Sections Initial temperature model and following.

Temperature boundary conditions: Sections Boundary temperature model and following.

Postprocessors: Sections Postprocess and following for most postprocessors, section Subsection: Postprocess / Visualization and following for postprocessors related to visualization.

The details of parameters in each of these categories can be found in the sections linked to above. Some of them will also be used in the cookbooks in Cookbooks.