Selection Terminology

A selection represents a set of entities on an entity dimension or geometric entity level. A boundary selection is a selection with the geometric entity level boundary. For a boundary selection in 3D the set of entities is face numbers and the entity dimension is 2. In 2D, a boundary selection has a set of edge numbers and the entity dimension is 1. There are no edge selection in 2D and 1D, and no point selection in 1D, because there are redundant with the boundary selection. The table below summarizes the geometric entity levels and their entity dimensions.

level	Dimension3D	Dimension 2D, 2D axisymmetric	Dimension 1D, 1D axisymmetric	Dimension 0D or global
Domain	3	2	1	N/A
Boundary	2	1	0	N/A
Edge	1	N/A	N/A	N/A
Point	0	0	N/A	N/A
Global	-1	-1	-1	-1

The geometric entity type, or just entity type, is a category in which each entity in a set belongs. Usually, the physics interface selection defines in what entity types an entity in a set belongs. Below is a short summary of all entity types available for features and selections.

Entity Type	Applies to Level(s)	Description
Active	All levels	Entities where the physics interface is active.
Inactive	All levels	Entities where the physics interface is inactive.
Geometry	All levels	Same as Active.
Exterior	Boundary	Entities that are exterior to the physics interface selection.
Interior	Boundary	Entities that are interior to the physics interface selection.
Symmetry axis	Boundary, Edge, Point	Only for axial symmetry. The entities that lies on the symmetry axis (z-axis).
Pair	Boundary, Edge, Point	Not used by entities. For a Feature it means that the program creates an automatic version for pairs.
Source or destination	All levels	Not used by entities. For a Feature it means it only applies as a fallback feature for pairs.
Exterior, neither source nor destination	Boundary	Not used by entities. For a Feature it means that it is excluded from the list of fallback features for pairs.
Neither source nor destination	Domain, Edge, Point	Same as the previous row for domains, edges, and points.
Identity pair	All levels	Entities that are identity pairs.
Contact pair	All levels	Entities that are contact pairs.
Perfectly matched layer	Domain	Domains that are perfectly matched layers,
Infinite element domain	Domain	Domains that are infinite elements domains.
Absorbing layer	Domain	Domains that are absorbing layers.
Scaled systems	Domain	Domains that are scaled systems.

Only a subset of these makes sense for a selection, and some are not used at all by the Physics Builder.