# Generalized arithmetic progression

(Redirected from Semilinear set)

In mathematics, a multiple arithmetic progression, generalized arithmetic progression, k-dimensional arithmetic progression or a linear set, is a set of integers or tuples of integers constructed as an arithmetic progression is, but allowing several possible differences. So, for example, we start at 17 and may add a multiple of 3 or of 5, repeatedly. In algebraic terms we look at integers

$a + mb + nc + \ldots$

where $a, b, c$ and so on are fixed, and $m, n$ and so on are confined to some ranges

$0$  ≤  $m$  ≤  $M$

and so on, for a finite progression. The number  $k$, that is the number of permissible differences, is called the dimension of the generalized progression.

More generally, let

$L(C;P)$

be the set of all elements $x$ in $N^n$ of the form

$x = c_0 + \sum_{i=1}^m k_i x_i,$

with $c_0$ in $C$, $x_1, \ldots, x_m$ in $P$, and $k_1, \ldots, k_m$ in $N$. $L$ is said to be a linear set if $C$ consists of exactly one element, and $P$ is finite.

A subset of $N^n$ is said to be semilinear if it is a finite union of linear sets.