Abstract:
For closed differential operators generated by quasi-elliptic systems of the first and second type, respectively, studied the properties of the spectrum. In the case of the conditions of the periodicity of the sequence of the eigenvector-functions of quasi-elliptic differential operator of the first type forms an orthonormal basis; the sequence of the eigenvector-functions of quasi-elliptic differential operator of the second type are either not full, orforms the basis of Riesz, that is certainly not an orthonormal basis.
Keywords:system of differential equations, boundary value problems, closed operators, spectrum, basis, orthogonal basis, a Riesz basis.
