Spectral parameter power series representation for solutions of linear system of two first order differential equations

A representation in the form of spectral parameter power series (SPPS) is given for a general solution of a one dimension Dirac system containing arbitrary matrix coefficient at the spectral parameter, BdY/dX + P(x)Y = lambda R(x)Y, where Y = (y(1), y(2))(T) is the unknown vector-function, lambda is the spectral parameter, B = (0 1 -1 0) , and P is a symmetric 2 x 2 matrix, R is an arbitrary 2 x 2 matrix whose entries are integrable complex-valued functions. The coefficient functions in these series are obtained by recursively iterating a simple integration process, beginning with a nonvanishing solution for one particular lambda = lambda(0). The existence of such solution is shown. For a general linear system of two first order differential equations P(x)dY/dx + Q(x)Y = lambda R(x)Y, x is an element of [a, b], where P, Q, R are 2 x 2 matrices whose entries are integrable complex-valued functions, P being invertible for every x, a transformation reducing it to a system (*) is shown. The general scheme of application of the SPPS representation to the solution of initial value and spectral problems as well as numerical illustrations are provided. (C) 2019 Elsevier Inc. All rights reserved.