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单词 FreeModule
释义

free module


Let R be a commutative ring with unity. A free moduleMathworldPlanetmathPlanetmath over Ris a (unital) module isomorphicPlanetmathPlanetmathPlanetmath to a direct sumMathworldPlanetmathPlanetmathPlanetmathPlanetmath of copies of R. In particular, as every abelian groupMathworldPlanetmath is a -module, a free abelian group is a direct sum of copies of . This is equivalentMathworldPlanetmathPlanetmathPlanetmathPlanetmath to saying that the module has a free basis,i.e. a set of elements with the that every element of the module can be uniquely expressed as an linear combinationMathworldPlanetmath over Rof elements of the free basis. In the case that a free module over R is a sum of finitely many copies of R, then the number of copies is called the rank of the free module.

An alternative definition of a free module is via its universal propertyMathworldPlanetmath: Given a set X, the free R-module F(X) on the set X is equipped with a function i:XF(X) satisfying the property that for any other R-module A and any function f:XA, there exists a unique R-module map h:F(X)A such that (hi)=f.

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更新时间:2025/5/4 16:57:06