# Spectrum of a ring

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A topological space whose points are the prime ideals of a ring with the Zariski topology (also called the spectral topology). It is assumed that is commutative and has an identity. The elements of can be regarded as functions on by setting  . supports a sheaf of local rings , called its structure sheaf. For a point , the stalk of over is the localization of at .

To any identity-preserving ring homomorphism there corresponds a continuous mapping . If is the nil radical of , then the natural mapping is a homeomorphism of topological spaces.

For a non-nilpotent element , let , where . Then the ringed spaces and , where is the localization of with respect to , are isomorphic. The sets are called the principal open sets. They form a basis for the topology on . A point is closed if and only if is a maximal ideal of . By assigning to its closure in , one obtains a one-to-one correspondence between the points of and the set of closed irreducible subsets of . is quasi-compact, but usually not Hausdorff. The dimension of is defined as the largest for which there is a sequence of distinct closed irreducible sets .

Many properties of can be described in terms of . For example, is Noetherian if and only if has the descending chain condition for closed sets; is an irreducible space if and only if is an integral domain; the dimension of coincides with the Krull dimension of , etc.

Sometimes one considers the maximal spectrum , which is the subspace of consisting of the closed points. For a graded ring one also considers the projective spectrum . If , then the points of are the homogeneous prime ideals of such that .

How to Cite This Entry:
Spectrum of a ring. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Spectrum_of_a_ring&oldid=15142
This article was adapted from an original article by L.V. Kuz'min (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article