Ising Renormalization Group

Block-spin decimation and RG flow in coupling space — phase transition as fixed point

Temperature K=J/kT0.44

External field h0.00

Metropolis sweeps50

RG: replace 2×2 blocks by majority vote. K_c ≈ 0.4407 (exact 2D Ising). Flow: K < K_c → high-T fixed point (disorder); K > K_c → low-T fixed point (order). Critical point = unstable fixed point.