Plancherel-Pólya's Type of Instability in Vibration System with Multiple Frozen Arguments

We discuss the problem of the inverse spectral problem of Sturm-Liouville operator with multiple frozen arguments at $\{a_{1}, a_{2},\ldots,a_{N}\}$ in $(0,π)$. One may consider the characteristic functions as perturbation of sine or of cosine functions depending on the boundary problem prescribed. However, such perturbation is represented in the form of Fourier transform of certain function which may or may not bring in Riesz basis theory and classical perturbation theory in functional analysis. We shall demonstrate the spectral perturbation in Plancherel-Pólya's type of inequality and connect to perturbation of related potential functions in $L^{2}$-functional norm.