Ising model

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Toy model of matter that exhibits <phase transition> in dimension 2 and greater. It does not provide numerically exact results by itself, but can serve as a tool to theorize existing and new <phase transitions>.

Each point in the lattice has two possible states: TODO insert image.

As mentioned at: https://stanford.edu/~jeffjar/statmech/intro4.html[] some systems which can be seen as modelled by it include:
* the spins direction (up or down) of atoms in a <magnet>, which can undergo phase transitions depending on temperature as that characterized by the <Curie temperature> and an externally applied magnetic field

  Neighboring spins like to align, which lowers the total system energy.
* the type of atom at a lattice point in a 2-metal <alloy>, e.g. <Fe-C> (e.g. <steel>). TODO: intuition for the neighbour interaction? What likes to be with what? And aren't different phases in different crystal structures?

Also has some funky relations to <renormalization> TODO.

Bibliography:
* https://stanford.edu/~jeffjar/statmech/intro4.html
