Commutative ring - Knowlpedia

A commutative ring is a ring $R$ such that $ab=ba$ for all $a,b\in R$ .

Remarks

Commutative rings support a particularly rich theory of ideals and spectrum-type constructions. In commutative rings, left/right distinctions for ideals and zero divisors disappear. Commutativity is independent of having a multiplicative identity: $2\mathbb Z$ is commutative but not unital.

Examples

$\mathbb Z$ and $\mathbb Q$ are commutative rings.
For a field $k$ , the polynomial ring $k[x_1,\dots,x_n]$ is commutative.
$M_n(k)$ for $n\ge 2$ is not commutative (matrix multiplication generally fails to commute).