Update model-guide.rst

[4er4er4er]

I am revising the modeling guide written by Gleb for MP-based solvers, based on updated categories that I developed for recent talks. I have already made some changes to the develop branch, but has become clear that continuing in that way would leave the guide potentially in a confusing state for a few weeks; thus I am working in a different branch from this point onward.

[glebbelov]

Both commits on model-guide.rst look fine to me.

If possible, let's avoid long-lived branches. In any case, let's merge regularly both ways, earlier = better.

[glebbelov]

Both commits on model-guide.rst look fine to me. Note that the 1st commit, being on the develop branch, is already online at amplmp.readthedocs.io.

If possible, let's avoid long-lived branches. In any case, let's merge regularly both ways, earlier = better.

[4er4er4er]

I am going to make some revisions now to the syntax terminology in the update branch (AMPL-MP-Modeling-Guide-Revised). This will temporarily cause some inconsistencies, so I won't make further commits until these revisions are done.

[gomfy]

• Under Expressions supported section, the sentences regarding extensions:
  How about introducing some bullet points? For example,

  MP automatically enables extensions, which support:

  • conditional, logical, or counting operators,
  • model transformations between equivalent problem classes (e.g. quadratic to linear),
  • native solver extensions.

  Regarding extensions handled by AMPL, are those not handled by MP? If not, then I think it would be useful to mention that.

• Under Expressions supported section/constr bullet point:
  There is an on missing after depending. The sentence should read:

  represents a constraint of the model, which may evaluate to true or false depending on the values of variables that it contains.

• Under Expressions supported section, last sentence:
  How about rephrasing it like below?

  AMPL represents these as expression trees, which are sent to MP-based solver interfaces to be processed as required by the underlying solver.