Add function to retrieve the current processed node in the branch-and-bound tree

[m-kahr]

Hi,
in the current documentation, I only found MOI.NodeCount() which returns the number of B&B nodes after the solving process. However, it would be great if one could also query the current processed node in a callback during the solving process.

kind regards, michael

[blegat]

Do you mean something like what @odow suggested in jump-dev/JuMP.jl#2127 (comment)?

[odow]

We won't be adding more attributes to MOI for callbacks. Use a solver-dependent callback instead (e.g., https://discourse.julialang.org/t/get-mipgap-in-gurobi-callbacks-jump-0-21/37232).

[m-kahr]

Do you mean something like what @odow suggested in JuliaOpt/JuMP.jl#2127 (comment)?

I mean something like you had in MathProgBase: MathProgBase.cbgetexplorednodes( cb )

Sometimes you want to do operations in callbacks, for instance, only every 10 processed nodes.

[odow]

Use a solver dependent callback, and call the appropriate solver-dependent method.

Alternatively, use something like

ncall = 0
function my_callback(cbdata)
    ncall += 1
    if mod(ncall, 10) != 0
        return
    end
    # ...
end

[odow]

Closing because we won't be adding new solver-independent attributes to MOI in the near-term (excluding #1112).