The Center (algebra) reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Center (algebra)

The term center is used in various contexts in abstract algebra to denote the set of all those elements that commute with all other elements. More specifically:

• The center of a ring R is the subset of R consisting of all those elements x of R such that xr = rx for all r in R. The center is a commutative subring of R, so R is an associative algebra over its center.
• The center of an associative algebra A consists of all those elements x of A such that xa = ax for all a in A.
• The center of a Lie algebra L consists of all those elements x in L such that [x,a] = 0 for all a in L. This is an ideal of the Lie algebra L.
• The center of a group G consists of all those elements x in G such that xg = gx for all g in G. This is a normal subgroup of G. See center of a group for more information.

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