TODO what it means to solve an Ising model in general?
stanford.edu/~jeffjar/statmech/lec4.html gives some good notions:
  • is the expectation value of the value. It is therefore a number between -1.0 an and 1.0, -1.0 means everything is always down, 0.0 means half up half down, and 1.0 means all up
  • : correlation between neighboring states. TODO.