Span (mathematics)

In algebra, the span of a set of elements of a module or vector space is the set of all finite linear combinations of that set: it may equivalently be defined as the intersection of all submodules or subspaces containing the given set.

For S a subset of an R-module M we have

$\langle S\rangle =\left\lbrace \sum _{i=1}^{n}r_{i}s_{i}:r_{i}\in R,~s_{i}\in S\right\rbrace =\bigcap _{S\subseteq N;N\leq M}N.\,$

We say that S spans, or is a spanning set for $\langle S\rangle$.

A basis is a linearly independent spanning set.

If S is itself a submodule then $S=\langle S\rangle$.

The equivalence of the two definitions follows from the property of the submodules forming a closure system for which $\langle \cdot \rangle$ is the corresponding closure operator.