Square lattice Ising model

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In statistical mechanics, the two-dimensional square lattice Ising model is a simple lattice model of interacting magnetic spins. The model is notable for having nontrivial interactions, yet having an analytical solution. The model was solved by Lars Onsager for the special case that the external magnetic field H = 0.^[1] An analytical solution for the general case for ${\displaystyle H\neq 0}$ has yet to be found.