Sawtooth Ising chain
= Sawtooth Ising chain
An <Ising model> on a chain of corner-sharing triangles, with one base <spin> and one apex <spin> per cell. If the apex interacts only with the two base corners, summing each apex independently gives a two-by-two <transfer matrix> on base <spins>. For symmetric <Ising spins> and <energy> $Jss'+\bar J\bar s(s+s')$, its entries are $2e^{-\beta Jss'}\cosh[\beta\bar J(s+s')]$.