A note on the matrix Sturm‐Liouville operators with principal functions

In this study, we take under investigation principal functions corresponding to the eigenvalues and the spectral singularities of the Operator L generated in L 2 ( R + , E ) by the differential expression l ( y ) = − y ′ ′ + Q ( x ) y , x ∈ R + : = [ 0 , ∞ ) and the boundary condition ( A 0  +  A 1 λ  +  A 2 λ 2 ) y ′ (0, λ ) − ( B 0  +  B 1 λ  +  B 2 λ 2 ) y (0, λ ) = 0, where Q is a matrix‐valued function and A i , B i , i  = 0,1,2 are non‐selfadjoint matrices also A 2 , B 2 are invertible.