On formal solutions of linear matrix differential-difference equations

In this paper, we construct a formal solution to the matrix differential-difference equation (dde) Y'(t) = A(t) Y(t(-1)), where A(t) is a matrix power series in t(-1). In many cases solutions to the latter equation and to the matrix differential equation Y' (t) = A (t)Y(t) have the same form. However, these solutions may have different forms when the spectrum of A(0), the leading term of A(t), contains -e(-1). (C) 2002 Published by Elsevier Science Inc. All rights reserved.