Enlargements of complexes of fixed size

Abstract

Let $A$ be an artin algebra. The aim of this work is to describe the enlargements of an indecomposable complex in $\mathbf{C}_{n}(\mbox{proj} \,A)$, and to study the irreducible morphisms between them. Precisely, we prove that any indecomposable complex in $\mathbf{C}_{[0,n]}(\mbox{proj} \,A)$ or in $\mathbf{C}_{n+1}(\mbox{proj} \,A)$ for $n$ a positive integer is a shift or an enlargement of an indecomposable complex in $\mathbf{C}_{n}(\mbox{proj} \,A)$. We also describe the entrances of the irreducible morphisms in $\mathbf{C}_{[0,n]}(\mbox{proj} \,A)$ between enlargements of an indecomposable complex $X$ in $\mathbf{C}_{n}(\mbox{proj} \,A)$.