© 1999 by London Mathematical Society
© The London Mathematical Society
Spectral Analysis of Higher-Order Differential Operators II: Fourth-Order Equations
FB Mathematik/Informatik, Universität Osnabrück 49069 Osnabrück, Germany. E-mail: christian.remling{at}mathematik.uni-osnabrueck.de
Received 21 May 1996. Revision received 9 September 1996.
We investigate the location and nature of the spectrum of the fourth-order self-adjoint equation
(p0 y'')''+(p1 y')'+qy=zwy
subject to certain asymptotic assumptions on the coefficients. The main tools are the theory of asymptotic integration and the TitchmarshWeyl M-matrix. Asymptotic integration yields asymptotic formulae for the solutions of the differential equation which are then used to derive properties of the M-matrix. The characterisation of spectral properties in terms of the boundary behaviour of M leads to the desired results.