On subinjectivity domains of pure-injective modules

Abstract

As an alternative perspective on the injectivity of a pure-injective module, a pure-injective module M is said to be pi-indigent if its subinjectivity domain is smallest possible, namely, consisting of exactly the absolutely pure modules. A module M is called subinjective relative to a module N if for every extension K of N, every homomorphism N \to M can be extended to a homomorphism K \to M. The subinjectivity domain of the module M is defined to be the class of modules N such that M is N-subinjective. Basic properties of the subinjectivity domains of pure-injective modules and of pi-indigent modules are studied. The structure of a ring over which every pure-injective (resp. simple, uniform, indecomposable) module is injective or subinjective relative only to the smallest possible family of modules is investigated. This work is a natural continuation to recent papers that have embraced the systematic study of the subinjective and subprojective domains of modules.