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homogeneous elements of a graded ring (Definition)

Let $k$ be a field, and let $R$ be a connected commutative $k$ -algebra graded by $\mb{N}^m$ . Then via the grading, we can decompose $R$ into a direct sum of vector spaces: $R=\coprod_{\omega\in\mb{N}^m} R_\omega$ , where $R_0=k$ .

For an arbitrary ring element $x\in R$ , we define the homogeneous degree of $x$ to be the value $\omega$ such that $x\in R_\omega$ , and we denote this by $\deg(x)=\omega$ . (See also homogeneous ideal)

A set of some importance (ironically), is the irrelevant ideal of $R$ , denoted by $R^+$ , and given by

$\displaystyle R_+=\coprod_{\omega\neq 0}R_\omega.$    

Finally, we often need to consider the elements of such a ring $R$ without using the grading, and we do this by looking at the homogeneous union of $R$ :
$\displaystyle \mathcal{H}(R)=\bigcup_\omega R_\omega.$    

In particular, in defining a homogeneous system of parameters, we are looking at elements of $\mathcal{H}(R_+)$ .

Bibliography

1
Richard P. Stanley, Combinatorics and Commutative Algebra, Second edition, Birkhauser Press. Boston, MA. 1986.




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See Also: homogeneous ideal

Also defines:  homogeneous element, homogeneous degree, irrelevant ideal, homogeneous union
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Cross-references: homogeneous system of parameters, homogeneous ideal, ring, vector spaces, direct sum, grading, commutative, connected, field
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This is version 3 of homogeneous elements of a graded ring, born on 2004-03-12, modified 2004-04-30.
Object id is 5694, canonical name is HomogeneousElementsOfAGradedRing.
Accessed 6825 times total.

Classification:
AMS MSC13A02 (Commutative rings and algebras :: General commutative ring theory :: Graded rings)

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