Lower bounds for the spectrum of ordinary differential operators
A special type of linear differential equations of even order is investigated. First, conditions for the associated minimal operator \(T_ 0\) to be bounded below are given and lower bounds for its Friedrich's extension as well as for the essential spectrum of self-adjoint extensions of \(T_ 0\) are given. From these bounds discreteness criteria for the spectrum are derived as are extensions of earlier results (of various authors).
linear differential equations of even order
scientific article; zbMATH DE number 3914755
scientific article