Definition:Algebra over Field

Definition
Let $F$ be a field.

An algebra over $F$ is an ordered pair $\left({A, *}\right)$ where:
 * $A$ is a vector space over $F$
 * $* : A^2 \to A$ is a bilinear mapping

That is, it is an algebra $\left({A, *}\right)$ over the ring $F$ where:
 * $F$ is a field
 * the $F$-module $A$ is a vector space.

Multiplication
The bilinear mapping $*$ is often called multiplication.

The symbol $A$ is often used for such an algebra, more so as the level of abstraction increases.

Also defined as
Some sources insist that an algebra over a field requires that the bilinear mapping $*$ must have an identity element $1_A$ such that:
 * $\forall a \in A: a * 1_A = 1_A * a = a$

... that is, that $\left({A, *}\right)$ has to be a unitary algebra.

It is worth being certain of what is meant in any works read.

Especially in commutative algebra, an algebra over a field is often defined as a unital associative commutative algebra.

Also known as
Some sources refer to an algebra over a field as a linear algebra.

Others call it a hypercomplex number system.

Also see

 * Definition:Algebra over Ring
 * Definition:Unitary Algebra
 * Definition:Associative Algebra