The ingredients are the four block operators and the four universe-block operators, which at the first iteration are 3 × × 3 matrices, the three left-site spin operators and the three right-site spin operators, which are always 3 × × 3 matrices. The Hamiltonian matrix of the superblock (the chain), which at the first iteration has only four sites, is formed by these operators. In the Heisenberg antiferromagnetic S=1 model the Hamiltonian is: