The paper deals with a method for accurate semisymbolic time-domain analysis of highly idealized linear lumped circuits. Pulse and step responses can be computed by means of the partial fraction decomposition. The procedure relies on an accurate computation of poles of the transfer function. The well known problem of the QR and QZ algorithms is their poor accuracy in the case of multiple roots. Moreover, the partial fraction decomposition itself is an ill-posed problem for closely-spaced clusters of roots. The method presented in this paper is based on an improved reduction procedure for transforming the generalized eigenproblem into a standard one in combination with an algorithm for computing the Jordan canonical form of inexact matrices.