Magnitude conjecture for representation-finite bound path algebras

Let Λ=kQ/I\Lambda=kQ/I be a representation-finite bound path algebra of rank nn, where the rank is the number of isomorphism classes of finitely generated indecomposable projective left Λ\Lambda-modules. Write χ(Λ\mhyphen ⁣mod)\chi({\Lambda}\mhyphen\!\operatorname{mod}) for the magnitude of the module category.

Magnitude conjecture.

  1. We have
χ(Λ\mhyphen ⁣mod)n.\chi({\Lambda}\mhyphen\!\operatorname{mod})\geq n.
  1. We have
χ(Λ\mhyphen ⁣mod)=n\chi({\Lambda}\mhyphen\!\operatorname{mod})=n

if and only if Λ\Lambda is special biserial.

The preceding results establish the equality for several important classes, including representation-finite special biserial algebras, string algebras, Nakayama algebras, and representation-finite local bound path algebras, as well as formulas for Dynkin and certain self-injective cases. The general inequality and the characterization of equality remain open.

Sources & referencesView supporting material

Primary source

Erlend D. Børve, Daniel Horiatakis and Martin Kalck, “Magnitude of module categories”, arXiv:2607.07555 (2026).

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