A localization is a universal functor from a given category CC with respect to the inversion of some family Σ\Sigma of morphisms in CC; sometimes one says also quotient category. In topos theory and some other subjects one often restricts to the situation when Σ\Sigma is a calculus of left fractions, and the corresponding localization functor has a right adjoint (which is then necessarily fully faithful); even more, one often requires that the localization functor is also left exact, hence exact.

Dual to that, othus, one often speaks of colocalization as the dual case (of the universal functor into the quotient category) where Σ\Sigma admits a calculus of right fractions and the corresponding quotient functor has a left adjoint. See also at right Bousfield localization.

The theory of colocalization in co-Grothendieck categories? has some features of its own as compared to the localization in Grothendieck categories. Namely, while by Gabriel-Popescu’s theorem, every Grothendieck category is a localization of a category of modules over a fixed unital ring, their dual categories may be presented in terms of the theory of linear topological rings with some compactness properties, which is the content of Gabriel-Oberst duality theory.


  • C. Năstăsescu, B. Torrecillas, Colocalization on Grothendieck categories with applications to coalgebras, J. Algebra 185 (1996), 108–124pdf available

A textbook exposition is in the chapter 6, Duality of

  • Nicolae Popescu, Abelian categories with applications to rings and modules, London Math. Soc. Monographs 3, Academic Press 1973. xii+467 pp. MR0340375

In derived and triangulated categories:

  • Shoham Shamir, Colocalization functors in derived categories and torsion theories, arxiv/0910.4724
  • Hvedri Inassaridze, Tamaz Kandelaki, Ralf Meyer, Localisation and colocalisation of triangulated categories at thick subcategories, arxiv/0912.2088
category: algebra

Last revised on April 23, 2015 at 18:52:10. See the history of this page for a list of all contributions to it.