Quirks in the hard-core lattice gas example

[gdalle]

• The $\infty$ sign mean in the energy formula might be a bit confusing, I would find it clearer to express the independent set constraint explicitly (unless the algorithm actually relies on this formulation with an objective barrier?)
• The lattice graphs are really cool but it's hard to distinguish shades of gray alone, could we maybe vary edge thickness too?
• The sampling step at the end returns an empty lattice

https://github.com/openjournals/joss-reviews/issues/5700

[mroavi]

Thanks for the suggestions! We've updated the energy formula, fixed the empty lattice issue, and tweaked the lattice graph's edge thickness. It now looks like this:

See the updated doc's page here.