Definition:Linear Combination

Linear Combination of Elements
Let $G$ be an $R$-module.

Let $\left \langle {a_n} \right \rangle$ be a sequence of elements of $G$.

An element $b \in G$ is a linear combination of $\left \langle {a_n} \right \rangle$ iff:
 * $\displaystyle \exists \left \langle {\lambda_n} \right \rangle \subseteq R: b = \sum_{k=1}^n \lambda_k a_k$

Linear Combination of a Subset
Let $\varnothing \subset S \subseteq G$.

Let $b \in G$ be a linear combination of some sequence $\left \langle {a_n} \right \rangle$ of elements of $S$.

Then $b$ is a linear combination of $S$.

Linear Combination of Null
$b$ is a linear combination of $\varnothing$ if $b = e_G$.

Also see
An integer combination is also called a linear combination. The definition is compatible with the one on this page.