 Real-space renormalization group

A real-space renormalization group replaces groups of microscopic degrees of freedom by retained coarse variables, summing over the eliminated variables to define a coarse Hamiltonian. The effective Boltzmann weights must preserve the partition function up to a tracked normalization. Spin decimation retains selected spins rather than forming an average block variable. Coarse-graining generally generates additional interactions, so closure of a chosen finite coupling family requires justification.