# Contact Properties

Properties are name-value pairs. Some properties are inheritable, which means that their values can be derived from surface properties of the two pieces. The PFC model guarantees that inheritable properties will be updated whenever the surface property of either piece is modified. The guarantee requires that the inheritable property has its inheritance flag set to true, and that both surface properties have the same name as the inheritable property. Properties of contacts can be specified directly with the contact property command. The surface properties of pieces, on the other hand, can be specified with the ball property, clump property, and wall property commands. Properties of contacts can also be specified directly by applying the CMAT to those contacts with the cmat apply command.

For each contact model, a properties table provides a concise property reference. The property table columns indicate:

1. the keyword (which indicates the keyword referring to the property to be used with appropriate commands or FISH functions);
2. the mathematical symbol (which coincides with the symbol used in the contact-model formulation);
3. a verbose description of the property;
4. the value type (see the table below);
5. the range over which the property may vary;
6. the default value;
7. whether or not the property is modifiable (all properties are readable, but only modifiable properties are writable); and
8. whether or not the property is inheritable.
Table 1: Value Type Designators
Type Description
BOOL Boolean value
INT integer number
FLT floating-point number
VEC 2D or 3D vector of floating-point numbers
VEC2 2D vector of floating-point numbers
VEC3 3D vector of floating-point numbers