Define addressing and linear addressing functions?

There are many data structures which can be represented so as to permit the referencing of any element by knowing its position in the structure.

The selection operation associated with such a structure is said to possess an addressing function.

An addressing function for a data structure consisting of n elements is a function which maps the ith element of the data structure onto an integer between one and n.

In the case of a vector, the addressing function f maps the ith element onto the integer I, which is a linear addressing function.