Ring (mathematics) by Ciro Santilli 34 Updated +Created
A Ring can be seen as a generalization of a field where:
Addition however has to be commutative and have inverses, i.e. it is an Abelian group.
The simplest example of a ring which is not a full fledged field and with commutative multiplication are the integers. Notably, no inverses exist except for the identity itself and -1. E.g. the inverse of 2 would be 1/2 which is not in the set. More specifically, the integers are a commutative ring.
A polynomial ring is another example with the same properties as the integers.
The simplest non-commutative, non-division is is the set of all 2x2 matrices of real numbers:
  • we know that 2x2 matrix multiplication is non-commutative in general
  • some 2x2 matrices have a multiplicative inverse, but others don't
Note that is not a ring because you can by addition reach the zero matrix.