Extensions of a New Algorithm for the Numerical Solution of Linear   Differential Systems on an Infinite Interval
  This paper is part of a series of papers in which the asymptotic theory and appropriate symbolic computer code are developed to compute the asymptotic expansion of the solution of an n-th order ordinary differential equation. The paper examines the situation when the matrix that appears in the Levinson expansion has a double eigenvalue. Application is made to a fourth-order ODE with known special function solution. 
B.M. Brown, M.S.P. Eastham, D.K.R. McCormack