Principal functions of non-selfadjoint discrete Sturm-Liouville equations with quadratic spectral parameter in boundary conditions

In this paper, we study the principal functions corresponding to the eigenvalues and the spectral singularities of the boundary value problem (BVP) a(n-1)y(n-1) + b(n)y(n) + a(n)y(n+1) = lambda y(n), n is an element of N (gamma(0) + gamma(1)lambda +.2.2)y(1) + (beta(0) + beta(1)lambda + beta(2)lambda(2))y(0) = 0, where (a(n)) and (b(n)), n is an element of N are complex sequences, gamma(i), beta(i) is an element of C, i = 0, 1, 2 and lambda is a eigenparameter.