Triangular Matrix Categories over path Categories and Quasi-hereditary Categories, as well as one point extensions by Projectives
In this paper, we prove that the lower triangular matrix category $Λ=\left [ \begin{smallmatrix} \mathcal{T}&0\\ M&\mathcal{U} \end{smallmatrix} \right ]$, where $\mathcal{T}$ and $\mathcal{U}$ are quasi-hereditary $\mathrm{Hom}$-finite Krull-Schmidt $K$-categories and $M$ is a $\mathcal U\otimes_K \mathcal T^{op}$-module that satisfies suitable conditions, is quasi-hereditary in the sense of \cite{LGOS1} and \cite{Martin}. Moreover, we solve the problem of finding quotients of path categories isomorphic to the lower triangular matrix category $Λ$, where $\mathcal T=K\mathcal{R/J}$ and $\mathcal U=K\mathcal{Q/I}$ are path categories of infinity quivers modulo admissible ideals. Finally, we study the case where $Λ$ is a path category of a quiver $Q$ with relations and $\mathcal U$ is the full additive subcategory of $Λ$ obtained by deleting a source vertex $*$ in $Q$ and $\mathcal T=\mathrm{add} \{*\}$. We then show that there exists an adjoint pair of functors $(\mathcal R, \mathcal E)$ between the functor categories $\mathrm{mod} \ Λ$ and $\mathrm{mod} \ \mathcal U$ that preserve orthogonality and exceptionality; see \cite{Assem1}. We then give some examples of how to extend classical tilting subcategories of $\mathcal U$-modules to classical tilting subcategories of $Λ$-modules.