EQUIVALENCE OF THE VARIATIONAL MATRIX PRODUCT METHOD AND THE DENSITY-MATRIX RENORMALIZATION-GROUP APPLIED TO SPIN CHAINS

We study the relationship between the Density Matrix :Renormalization Group (DMRG) and the variational matrix product method (MPM). In the l atter method one can also define a density matrix whose eigenvalues tu rn out to be numerically close to those of the DMRG. We illustrate our ideas with the spin-1 Heisenberg chain, where we compute the ground-s tate energy and the spin correlation length. We also give a rotational invariant formulation of the MPM.