Table 1 The Euler characteristic \(\chi \) and the generalized Euler characteristic \(\chi _{G}\) predicted for the microwave networks \(\Gamma (6,8,|V_D|=0,1,2)\) for four combinations of Neumann (N) and Dirichlet (D) boundary conditions (BC) on the two tail-like edges \(l_{2,5}\) and \(l_{4,6}\).

From: A new spectral invariant for quantum graphs

\(\text{ BC: } l_{2,5}\)

\(\text{ BC: } l_{4,6}\)

\(\;\;\; \chi \;\;\;\)

\(\;\; \chi _G \;\; \)

N

N

\(-2\)

N

D

\(-3\)

D

N

\(-3\)

D

D

\(-4\)