Definition:Rank Function (Matroid)

Definition
Let $M = \struct{S, \mathscr I}$ be a matroid.

The rank function of $M$ is the mapping $\rho : \powerset S \to \Z$ from the power set of $S$ into the integers defined by:
 * $\forall A \subseteq S : \map \rho A = \max \set{ \size A : X \subseteq A \land X \in \mathscr I }$

where $\size A$ denotes the cardinality of $A$.