For 10 points, name this model of statistical mechanics.
A problem associated with this model asks for the number of color patterns for a rectangular grid of red and green unit squares given a prescribed number of boundary edges. Unlike in the (*) Heisenberg model, spin direction is fixed and the spin variable can only assume two values. When the interaction between neighboring spins favors anti-parallel alignment, the ordered state is anti-ferromagnetic instead of ferromagnetic. For 10 points, name this model of statistical mechanics.
A problem associated with this model asks for the number of color patterns for a rectangular grid of red and green unit squares given a prescribed number of boundary edges.
{Ising} model