Traces of semi-invariants

This article investigates the traces of certain modules over rings of invariants associated with finite groups. More precisely, we provide a formula for computing the traces of arbitrary semi-invariants, thereby contributing to the understanding of the non-Gorenstein locus of rings of invariants. Additionally, we discuss applications of this formula, including criteria for rings of invariants to be Gorenstein on the punctured spectrum and nearly Gorenstein, as well as criteria for semi-invariants to be locally free.