Comparing $\mathrm{Add}(M)$ with $\mathrm{Prod}(M)$

Abstract

We present characterizations for the inclusions $\mathrm{Add}(M)\subseteq \mathrm{Prod}(M)$ and $\mathrm{Prod}(M)\subseteq \mathrm{Add}(M)$ in locally finitely presented categories and in compactly generated triangulated categories. As applications, we describe the situations when the classes of the form $\mathrm{Prod}(M)$ and $\mathrm{Add}(M)$ are (pre)covering, respectively (pre)enveloping.