|
In mathematics, a Grothendieck category is a certain kind of abelian category, introduced in Alexander Grothendieck's Tôhoku paper of 1957〔. (English translation ).〕 in order to develop the machinery of homological algebra for modules and for sheaves in a unified manner. To every algebraic variety one can associate a Grothendieck category , consisting of the quasi-coherent sheaves on . This category encodes all the relevant geometric information about , and can be recovered from . This example gives rise to one approach to noncommutative algebraic geometry: the study of "non-commutative varieties" is then nothing but the study of Grothendieck categories.〔(【引用サイトリンク】author=Izuru Mori )〕 ==Definition== By definition, a Grothendieck category is an AB5 category with a generator. Spelled out, this means that * is an abelian category; * every (possibly infinite) family of objects in has a coproduct (a.k.a. direct sum) in ; * direct limits (a.k.a. filtered colimits) of exact sequences are exact; this means that if a direct system of short exact sequences in is given, then the induced sequence of direct limits is a short exact sequence as well. (Direct limits are always right-exact; the important point here is that we require them to be left-exact as well.) * possesses a generator, i.e. there is an object in such that is a faithful functor from to the category of sets. (In our situation, this is equivalent to saying that every object of admits an epimorphism , where denotes a direct sum of copies of , one for each element of the (possibly infinite) set .) 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Grothendieck category」の詳細全文を読む スポンサード リンク
|