= Migdal-Kadanoff approximation
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= Migdal-Kadanoff approach
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A real-space approximation that moves or combines lattice bonds so that selected intermediate spins can be summed through a chain recursion. On a one-dimensional nearest-neighbour <Ising model>, no transverse <bond moving> is needed and <exact zero-field Ising-chain decimation> closes exactly. In higher dimensions, neglected geometric <correlations> generally make the transformed model approximate on the original lattice. The order of <bond moving> and decimation must be stated; the two operations need not commute. The bond-moving-first convention is described in <Position Space Renormalization Group by Mehran Kardar> lecture 14, section V.D.
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