nLab homotopy coproduct


Homotopy coproducts are a special case of homotopy colimits, when the indexing diagram is a discrete category.

Homotopy coproducts can be defined in any relative category, just like homotopy colimits, but practical computations are typically carried out in presence of additional structures such as model structures.


In any model category, the homotopy coproduct of a family of objects {A i} iI\{A_i\}_{i\in I} can be computed by cofibrantly replacing? each A iA_i and computing the (ordinary) coproduct of the resulting family {QA i} iI\{QA_i\}_{i\in I} of cofibrant replacements.

If weak equivalences are closed under small coproducts, then homotopy coproducts can be computed as ordinary coproducts, because the map iIQA i iIA i\coprod_{i\in I}QA_i\to \coprod_{i\in I}A_i is a weak equivalence.


In simplicial sets with simplicial weak equivalences, topological spaces with weak homotopy equivalences, and chain complexes with quasi-isomorphisms, homotopy coproducts can be computed as ordinary coproducts because weak equivalences are closed under small coproducts.

In commutative differential graded algebras with quasi-isomorphisms homotopy coproducts can be computed by resolving each object by a cofibrant commutative differential graded algebra?, and then computing their ordinary tensor product.

Last revised on September 30, 2022 at 21:08:57. See the history of this page for a list of all contributions to it.