A formula for regularized sums of eigenvalues of a Sturm–Liouville problem with delayed argument at the point of discontinuity is obtained. Moreover, nodal points of the related problem are investigated.
"Spectrum, trace and nodal points of a Sturm–Liouville type delayed differential operator with interface conditions." Rocky Mountain J. Math. 51 (1) 283 - 294, February 2021. https://doi.org/10.1216/rmj.2021.51.283