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For example, if R is a commutative ring and f an element in R, then the localization [] consists of elements of the form /,, (to be precise, [] = [] / ().) [42] The localization is frequently applied to a commutative ring R with respect to the complement of a prime ideal (or a union of prime ideals) in R .
As an example, the nilradical of a ring, the set of all nilpotent elements, is not necessarily an ideal unless the ring is commutative. Specifically, the set of all nilpotent elements in the ring of all n × n matrices over a division ring never forms an ideal, irrespective of the division ring chosen. There are, however, analogues of the ...
that associates to each element of R its equivalence class is a surjective ring homomorphism that has the ideal as its kernel. [8] Conversely, the kernel of a ring homomorphism is a two-sided ideal. Therefore, the two-sided ideals are exactly the kernels of ring homomorphisms.
In ring theory, a branch of mathematics, an idempotent element or simply idempotent of a ring is an element a such that a 2 = a. [1] [a] That is, the element is idempotent under the ring's multiplication. Inductively then, one can also conclude that a = a 2 = a 3 = a 4 = ... = a n for any positive integer n.
In a nonzero ring, the element 0 is not a unit, so R × is not closed under addition. A nonzero ring R in which every nonzero element is a unit (that is, R × = R ∖ {0}) is called a division ring (or a skew-field). A commutative division ring is called a field. For example, the unit group of the field of real numbers R is R ∖ {0}.
A ring R is a local ring if it has any one of the following equivalent properties: R has a unique maximal left ideal. R has a unique maximal right ideal. 1 ≠ 0 and the sum of any two non-units in R is a non-unit. 1 ≠ 0 and if x is any element of R, then x or 1 − x is a unit.
Examples. In the non-unital ring of even integers, (6) is regular (=) while (4) is not. Let M be a simple right A-module. If x is a nonzero element in M, then the annihilator of x is a regular maximal right ideal in A. If A is a ring without maximal right ideals, then A cannot have even a single modular right ideal.
There are finite noncommutative rings: for example, the n-by-n matrices over a finite field, for n > 1. The smallest noncommutative ring is the ring of the upper triangular matrices over the field with two elements; it has eight elements and all noncommutative rings with eight elements are isomorphic to it or to its opposite. [1]