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In algebra, a unit or invertible element [a] of a ring is an invertible element for the multiplication of the ring. That is, an element u of a ring R is a unit if there exists v in R such that = =, where 1 is the multiplicative identity; the element v is unique for this property and is called the multiplicative inverse of u.
The set of units of a ring is a group under ring multiplication; this group is denoted by R × or R* or U(R). For example, if R is the ring of all square matrices of size n over a field, then R × consists of the set of all invertible matrices of size n , and is called the general linear group .
If S is an integral extension of a commutative ring R, then S and R have the same dimension. Closely related concepts are those of depth and global dimension. In general, if R is a noetherian local ring, then the depth of R is less than or equal to the dimension of R. When the equality holds, R is called a Cohen–Macaulay ring.
In algebraic number theory, a fundamental unit is a generator (modulo the roots of unity) for the unit group of the ring of integers of a number field, when that group has rank 1 (i.e. when the unit group modulo its torsion subgroup is infinite cyclic).
In the theory of rings, a branch of abstract algebra, it is described as the group of units of the ring of integers modulo n. Here units refers to elements with a multiplicative inverse, which, in this ring, are exactly those coprime to n.
unit or invertible element : An element r of the ring R is a unit if there exists an element r −1 such that rr −1 = r −1 r = 1. This element r −1 is uniquely determined by r and is called the multiplicative inverse of r .
In mathematics, Dirichlet's unit theorem is a basic result in algebraic number theory due to Peter Gustav Lejeune Dirichlet. [1] It determines the rank of the group of units in the ring O K of algebraic integers of a number field K. The regulator is a positive real number that determines how "dense" the units are.
An element of ring is called a unit if it possesses a multiplicative inverse. Another particular type of element is the zero divisors , i.e. an element a {\displaystyle a} such that there exists a non-zero element b {\displaystyle b} of the ring such that a b = 0 {\displaystyle ab=0} .