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单词 FractionalIdealOfCommutativeRing
释义

fractional ideal of commutative ring


Definition.  Let R be a commutative ring having a regular elementPlanetmathPlanetmathPlanetmath and let T be the total ring of fractionsMathworldPlanetmath of R.  An R-submodule (http://planetmath.org/Submodule) 𝔞 of T is called fractional idealMathworldPlanetmathPlanetmath of R, provided that there exists a regular element d of R such that  𝔞dR.  If a fractional ideal is contained in R, it is a usual ideal of R, and we can call it an integral ideal of R.

Note that a fractional ideal of R is not necessarily a subring of T.  The set of all fractional ideals of R form under the multiplication an commutative semigroup with identity elementMathworldPlanetmathR=R+e,  where e is the unity of T.

An ideal 𝔞 ( or fractional) of R is called invertible, if there exists another ideal 𝔞-1 of R such that  𝔞𝔞-1=R.  It is not hard to show that any invertible ideal 𝔞 is finitely generatedMathworldPlanetmathPlanetmath and regular (http://planetmath.org/RegularIdeal), moreover that the inverse ideal 𝔞-1 is uniquely determined (see the entry “invertible ideal is finitely generated (http://planetmath.org/InvertibleIdealIsFinitelyGenerated)”) and may be generated by the same amount of generatorsPlanetmathPlanetmath (http://planetmath.org/GeneratorsOfInverseIdeal) as 𝔞.

The set of all invertible fractional ideals of R forms an Abelian groupMathworldPlanetmath under the multiplication.  This group has a normal subgroupMathworldPlanetmath consisting of all regular principal fractional ideals; the corresponding factor group is called the of the ring R.

Note.  In the special case that the ring R has a unity 1, R itself is the principal idealMathworldPlanetmathPlanetmath (1), being the identity element of the semigroup of fractional ideals and the group of invertible fractional ideals.  It is called the unit ideal.  The unit ideal is the only integral ideal containing units of the ring.

Titlefractional ideal of commutative ring
Canonical nameFractionalIdealOfCommutativeRing
Date of creation2015-05-06 14:40:32
Last modified on2015-05-06 14:40:32
Ownerpahio (2872)
Last modified bypahio (2872)
Numerical id16
Authorpahio (2872)
Entry typeDefinition
Classificationmsc 13B30
Related topicFractionalIdeal
Related topicGeneratorsOfInverseIdeal
Related topicIdealClassesFormAnAbelianGroup
Definesfractional ideal
Definesintegral ideal
Definesinvertible ideal
Definesinvertible
Definesinverse ideal
Definesclass groupMathworldPlanetmath of a ring
Definesunit ideal
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