  Dukelsky, Mart\'in-Delgado, Nishino and Sierra (Europhys. Lett., 43, 457
(1998) - hereafter referred to as DMNS) investigated the matrix product method
(MPM), comparing it with the infinite-size density matrix renormalization group
(DMRG). For equivalent basis size, the MPM produces an improved variational
energy over that produced by DMRG and, unlike DMRG, produces a
translationally-invariant wavefunction. The DMRG results presented were
significantly worse than the MPM, caused by a shallow bound state appearing at
the join of the two DMRG blocks. They also suggested that the DMRG results can
be improved by using an alternate superblock construction $[B] \bullet [B]$ for
the last few steps of the calculation. In this comment, we show that the DMRG
results presented by DMNS are in error and the artificial bound state produced
by the standard superblock configuration is very small even for $m=2$ states
kept. In addition, we calculate explicitly the energy and wavefunction for the
$[B] \bullet [B]$ superblock structure and verify that the energy coincides
with that of the MPM, as conjectured by S. Ostlund and S. Rommer (Phys. Rev.
Lett., 75, 3537 (1995)).
