Representation dimensions of triangular matrix algebras

TL;DR

This paper investigates the representation dimensions of triangular matrix algebras derived from hereditary algebras, establishing bounds based on the algebra's type and characterizing when certain endomorphism algebras are representation finite.

Contribution

It provides bounds for the representation dimension of triangular matrix algebras and characterizes when endomorphism algebras of tilting modules are representation finite.

Findings

rep.dim T_2(A) ≤ 3 for Dynkin type A

rep.dim T_2(A) ≤ 4 for non-Dynkin type A

End_{A^{(1)}}(T̄) is representation finite iff a certain subcategory is of finite type

Abstract

Let $A$ be a finite dimensional hereditary algebra over an algebraically closed field $k$, $T_2(A)=(\begin{array}{cc}A&0 A&A\end{array})$ be the triangular matrix algebra and $A^{(1)}=(\begin{array}{cc}A&0 DA&A\end{array})$ be the duplicated algebra of $A$ respectively. We prove that ${\rm rep.dim}\ T_2(A)$ is at most three if $A$ is Dynkin type and ${\rm rep.dim}\ T_2(A)$ is at most four if $A$ is not Dynkin type. Let $T$ be a tilting A-$\module$ and $\ol{T}=T\oplus\ol{P}$ be a tilting $A^{(1)}$-$\module$. We show that $\End_{A^{(1)}} \ol{T}$ is representation finite if and only if the full subcategory $\{(X,Y,f)\ |\ X\in {\rm mod}\ A, Y\in\tau^{-1}\mathscr{F}(T_A)\cup{\rm add}\ A\}$ of ${\rm mod \ T_2(A)}$ is of finite type, where $\tau$ is the Auslander-Reiten translation and $\mathscr{F}(T_A)$ is the torsion-free class of ${\rm mod}\ A$ associated with $T$. Moreover, we also prove that ${\rm rep.dim\ End}_{A^{(1)}}\ {\ol T}$ is at most three if $A$ is Dynkin type.