Filtered objects in extriangulated categories

Abstract

Let $R$ be an artin ring and $\Theta=\{\Theta(1),\Theta(2),\cdots,\Theta(n)\}$ be a family of objects in an artin extriangulated $R$-category $(\cal C,\mathbb{E},\mathfrak{s})$ such that $\mathbb{E}(\Theta(j),\Theta(i))=0$ for all $j\geq i$. In this paper, we show that the class $\cal P(\Theta)$ of the $\Theta$-projective objects is a precovering class and the class $\cal I(\Theta)$ of the $\Theta$-injective objects is a preenveloping one in $\cal C$. Furthermore, if $\cal C$ has enough projectives and enough injectives, we show that the subcategory $\cal F(\Theta)$ of $\Theta$-filtered objects is functorially finite in $\cal C$. As an appliacation, this generalizes the works by Ringel in a module category case and Mendoza-Santiago in a triangulated category case.