Singular locally-scalar representations of quivers in Hilbert spaces and separating functions

Abstract

A numeric function $\rho$: $\rho(k)=1+\frac{k-1}{k+1}, k \in N$ was considered in [1]. In its terms criterions of finite representability and tameness of marked quivers, posets with equivalence and dyadic posets can be obtained; Dynkin schemes and extended schemes also can be characterized. In this paper authors consider the connection of function $\rho$ with locally-scalar representations [2] of extended Dynkin graphs. Then a family of functions $\rho_n$ is defined -- a generalization of function $\rho$, which plays an analogous part for more wide class of graphs. Also some properties of functions $\rho$ and $\rho_k$ are proved. References [1] L.A. Nazarova, A.V. Roiter. {\it Norm of a relation, separating functions and representations of marked quivers.} Ukr. Math. Jour., 54(2002), No.6, p.808-840. [2] S.A. Kruglyak, A.V. Roiter. {\it Locally-scalar representations of graphs in the category of Hilbert spaces.} Prepr. Ukr. Math. Jour. (2003).