# JuMP 0.18 + CPLEX: How to force user cuts?

**URL:** <https://discourse.julialang.org/t/jump-0-18-cplex-how-to-force-user-cuts/23659>\
**Category:** Optimization (Mathematical)\
**Created:** [April 29, 2019, 4:01pm UTC](https://discourse.julialang.org/t/jump-0-18-cplex-how-to-force-user-cuts/23659 "2019-04-29T16:01:01Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![mike\_k](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mike_k/32/211864_2.png) [@mike\_k](https://discourse.julialang.org/u/mike_k)\
**Post date:** [April 29, 2019, 4:01pm UTC](https://discourse.julialang.org/t/jump-0-18-cplex-how-to-force-user-cuts/23659/1 "2019-04-29T16:01:01Z")

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Dear community,

is there any way to force CPLEX to add all user cuts (i.e., passing the option `CPX_USECUT_FORCE`)?

Here [https://github.com/JuliaOpt/CPLEX.jl/blob/master/src/cpx\_callbacks.jl](https://github.com/JuliaOpt/CPLEX.jl/blob/master/src/cpx_callbacks.jl) the option seems to be hard-coded to `CPX_USECUT_PURGE`, but I want to avoid changing the parameter in the source code of the package.

Thank you in advance!!

* * *

UPDATE:  
I now changed the parameters manually in the source to `CPX_USECUT_FORCE` at line 62/65 in the `cpx_callbacks.jl` but this did not solve my problem:  
I have an ILP model in which I use lazy and user callbacks and I want to add user cuts as long as I find some before branching starts. In particular I am interested in the root relaxation. In an minimal instance there are 3 user cuts. However, the user callback is only called once and therefore the last two cuts are not added.

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**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [April 29, 2019, 8:42pm UTC](https://discourse.julialang.org/t/jump-0-18-cplex-how-to-force-user-cuts/23659/2 "2019-04-29T20:42:38Z")

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I suggest manually modifying the source until you get something that works.

Note that `CPX_USECUT_FORCE` will only guarantee that if a cut is added, it will not be purged later on in the solve. It doesn’t guarantee that the callback will be called in the first place.

I don’t think you can control when and how many times CPLEX decides to call your callback.

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**Author:** ![mike\_k](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mike_k/32/211864_2.png) [@mike\_k](https://discourse.julialang.org/u/mike_k)\
**Post date:** [April 30, 2019, 7:23am UTC](https://discourse.julialang.org/t/jump-0-18-cplex-how-to-force-user-cuts/23659/3 "2019-04-30T07:23:51Z")

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Thank you for the reply. I now had a closer look, and it seems that even the first user cut is not added. At least I know from the C++ interface that the LP relaxation is resolved if a new user cut is added, which does not happen in my case. I.e, Since I stop the algorithm right after the root node, I obtain the same results with only lazy cuts and with both, lazy and user cuts. However, adding the user cuts manually (hard-coded) to the model works fine.  
In the callback I add the cuts with

```julia
@usercut( cb, model[:u][w] <= C + dot(c, model[:z]) )

```

where :u and :z are decision vectors, C is a constant c a vector, and `cb::CPLEX.CplexCutCallbackData`.

Is there maybe anything wrong with that, or are there some other parameters that force to resolve the LP relaxation after a cut is added?

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**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [April 30, 2019, 7:22pm UTC](https://discourse.julialang.org/t/jump-0-18-cplex-how-to-force-user-cuts/23659/4 "2019-04-30T19:22:19Z")

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In JuMP 0.19, we have (temporarily) removed solver-independent callbacks because the implementations differ between solvers and it is almost always necessary to have more direct control over the callback than JuMP 0.18 provides.

Your example is a good demonstration of this.

`CPLEX.jl` wraps the C interface, so in theory, anything you can do via C you can do via `CPLEX.jl`. So I would look through the C documentation for inspiration on what to do. I don’t have any concrete advice as I don’t know all the parameters (there are many).

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**Author:** ![mike\_k](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mike_k/32/211864_2.png) [@mike\_k](https://discourse.julialang.org/u/mike_k)\
**Post date:** [May 1, 2019, 7:07am UTC](https://discourse.julialang.org/t/jump-0-18-cplex-how-to-force-user-cuts/23659/5 "2019-05-01T07:07:46Z")

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Okay, this sounds like bad news to me. Thank you anyway @odow.