Debug features in callbacks

[joehuchette]

This is kind of a cool idea from @IainNZ JuMPeR that would (1) be easy to implement, and (2) more elegant than littering a callback with print statements IMO, especially with more complex logic/multiple cuts. The idea is just to print out all cuts that get added (or heurstic solutions, or branches...) in a nice little block. See https://github.com/IainNZ/JuMPeR.jl/blob/0bd4b43bb53ef5545b0f3e4df19378c64387483e/src/oracle_poly.jl#L139

[mlubin]

Yes, we could pretty easily do this. Just need a nice syntax for it.

[joehuchette]

Keyword argument? Either in the solve call or when setting lazy/user/heuristic callback

[joehuchette]

(Probably solve, verbose_callback=true)

[mlubin]

What about a keyword argument when adding the constraint itself instead of adding any extra state:

@addLazyConstraint(m, x+y <= 2, print_constraint=true)

This is simpler but not quite as pretty.

[joehuchette]

It is simpler, but at that point I'm not sure it's worth the effort rather than just doing a println(x+y<=2), especially since callback constraints are often build up in pieces. I'm thinking we mark this for a later release and take some time to think about how to do this in a really cool way.

[chriscoey]

@joehuchette any new thoughts on this? and see JuliaOpt/MathProgBase.jl#170

[joehuchette]

Not really, I think something like addlazycallback(m, func, verbose=true) is reasonable and would be a nice addition.

[mlubin]

Resolved vacuously. Callbacks don't happen here anymore, but this is still a useful idea for the solver-specific callbacks.