Definition:Linear Span

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Let $V$ be a vector space over $K$.

Let $A \subseteq V$ be a subset of $V$.

Then the linear span of $A$, denoted $\span A$ or $\map \span A$, is the set:

$\ds \set {\sum_{k \mathop = 1}^n \alpha_k f_k: n \in \N_{\ge 1}, \alpha_i \in K, f_i \in A}$

The linear span can be interpreted as the set of all linear combinations (of finite length) of these vectors.

Definition for $\R^n$

In $\R^n$ (where $n \in \N_{>0}$), above definition translates to:

$\ds \map \span {\mathbf v_1, \mathbf v_2, \dotsc, \mathbf v_k} = \set {\sum_{i \mathop = 1}^k \ c_i \ \mathbf v_i: c_i \in \R, \mathbf v_i \in \R^n, 1 \le i \le k}$

Also denoted as

One also frequently encounters the notation $\sequence A$.

Typically, when $A$ is small, this is also written by substituting the braces for set notation by angle brackets.

For example, when $A = \set {x_1, x_2}$, one writes $\sequence {x_1, x_2}$ for $\span A$.

On this site, the notations using $\span$ are preferred, so as to avoid possible confusion.

Also see