Density matrix renormalization group for 19-vertex model

We embody the density matrix renormalization group method for the 19-vertex model on a square lattice; the 19-vertex model is regarded to be equivalent to the XY model for small interaction. The transfer matrix of the 19-vertex model is classified by the total number of arrows incoming into one layer of the lattice. By using this property, we reduce the dimension of the transfer matrix appearing in the density matrix renormalizaion group method and obtain a very nice value of the conformal anomaly which is consistent with the value at the Berezinskii-Kosterlitz-Thouless transition point. Keyword : Kosterlitz-Thouless, Renormalization group