Definition:Linear Span

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Let $V$ be a vector space over $K$, and let $A \subseteq V$ be a subset.

Then the linear span of $A$, denoted $\operatorname{span} A$ or $\operatorname{span} \left({A}\right)$, is the set

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

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:

$\displaystyle \operatorname{span}\left({\mathbf v_1,\mathbf v_2,\cdots,\mathbf v_k}\right) = \left\{ {\sum_{i \mathop = 1}^k \ c_i \ \mathbf v_i: c_i \in \R, \mathbf v_i\in \R^n, 1 \le i \le k} \right \}$

Also denoted as

One also frequently encounters the notation $\left\langle{A}\right\rangle$.

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

For example, when $A = \left\{{x_1, x_2}\right\}$, one writes $\left\langle{x_1, x_2}\right\rangle$ for $\operatorname{span} A$.

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

Also see