# Lazyconstraint not defined using GLPK solver callbacks
**URL:** https://discourse.julialang.org/t/lazyconstraint-not-defined-using-glpk-solver-callbacks/34012
**Category:** Optimization (Mathematical)
**Tags:** question
**Created:** [January 31, 2020, 8:39am UTC](https://discourse.julialang.org/t/lazyconstraint-not-defined-using-glpk-solver-callbacks/34012 "2020-01-31T08:39:22Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Espenol](https://discourse.julialang.org/u/Espenol)
#### Post date: [January 31, 2020, 8:39am UTC](https://discourse.julialang.org/t/lazyconstraint-not-defined-using-glpk-solver-callbacks/34012/1 "2020-01-31T08:39:22Z")
Hello! Sorry about the newb question, but I have an issue setting lazy constraint.
I follow the example [here](http://www.juliaopt.org/JuMP.jl/0.18/callbacks.html) but don’t have access to licensed solvers so I use the GLPK solver instead of the Gurobi solver by applying the following two commands:
`using GLPK` and `m=Model(with_optimizer(GLPK.Optimizer))`
It seems that the functions are not in scope, and I get the following error messages:
`LoadError: LoadError: UndefVarError: @lazyconstraint not defined`
If I comment out “@lazyconstraint”, I get the following error message:
`LoadError: UndefVarError: addlazycallback not defined`
Because of these errors I attempted to check if my packages are correctly installed. If I run
`(v1.3) pkg> test GLPK` I get the output below, where specifically there is an error in the `GLPK\HjJiX\test\MOI_callbacks.jl:1` file.
How do I fix this problem? Thank you for your time and attention!
````julia
(v1.3) pkg> test GLPK
Testing GLPK
Resolving package versions...
Status `C:\Users\espenhs\AppData\Local\Temp\jl_hTU9s6\Manifest.toml`
[6e4b80f9] BenchmarkTools v0.4.3
[b99e7846] BinaryProvider v0.5.8
[523fee87] CodecBzip2 v0.6.0
[944b1d66] CodecZlib v0.6.0
[60bf3e95] GLPK v0.12.1
[cd3eb016] HTTP v0.8.8
[83e8ac13] IniFile v0.5.0
[682c06a0] JSON v0.21.0
[7d188eb4] JSONSchema v0.2.0
[b8f27783] MathOptInterface v0.9.9
[739be429] MbedTLS v0.7.0
[d8a4904e] MutableArithmetics v0.2.2
[bac558e1] OrderedCollections v1.1.0
[69de0a69] Parsers v0.3.10
[3bb67fe8] TranscodingStreams v0.9.5
[2a0f44e3] Base64 [`@stdlib/Base64`]
[ade2ca70] Dates [`@stdlib/Dates`]
[8ba89e20] Distributed [`@stdlib/Distributed`]
[b77e0a4c] InteractiveUtils [`@stdlib/InteractiveUtils`]
[8f399da3] Libdl [`@stdlib/Libdl`]
[37e2e46d] LinearAlgebra [`@stdlib/LinearAlgebra`]
[56ddb016] Logging [`@stdlib/Logging`]
[d6f4376e] Markdown [`@stdlib/Markdown`]
[a63ad114] Mmap [`@stdlib/Mmap`]
[de0858da] Printf [`@stdlib/Printf`]
[9a3f8284] Random [`@stdlib/Random`]
[ea8e919c] SHA [`@stdlib/SHA`]
[9e88b42a] Serialization [`@stdlib/Serialization`]
[6462fe0b] Sockets [`@stdlib/Sockets`]
[2f01184e] SparseArrays [`@stdlib/SparseArrays`]
[10745b16] Statistics [`@stdlib/Statistics`]
[8dfed614] Test [`@stdlib/Test`]
[4ec0a83e] Unicode [`@stdlib/Unicode`]
Test Summary: | Pass Total
C API | 163 163
MathOptInterface: Error During Test at C:\Users\espenhs\.julia\packages\GLPK\HjJiX\test\runtests.jl:20
Got exception outside of a @test
LoadError: ArgumentError: Package Random not found in current path:
- Run `import Pkg; Pkg.add("Random")` to install the Random package.
Stacktrace:
[1] require(::Module, ::Symbol) at .\loading.jl:887
[2] include at .\boot.jl:328 [inlined]
[3] include_relative(::Module, ::String) at .\loading.jl:1105
[4] include(::Module, ::String) at .\Base.jl:31
[5] include(::String) at .\client.jl:424
[6] top-level scope at C:\Users\espenhs\.julia\packages\GLPK\HjJiX\test\runtests.jl:22
[7] top-level scope at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Test\src\Test.jl:1107
[8] top-level scope at C:\Users\espenhs\.julia\packages\GLPK\HjJiX\test\runtests.jl:21
[9] include at .\boot.jl:328 [inlined]
[10] include_relative(::Module, ::String) at .\loading.jl:1105
[11] include(::Module, ::String) at .\Base.jl:31
[12] include(::String) at .\client.jl:424
[13] top-level scope at none:6
[14] eval(::Module, ::Any) at .\boot.jl:330
[15] exec_options(::Base.JLOptions) at .\client.jl:263
[16] _start() at .\client.jl:460
in expression starting at C:\Users\espenhs\.julia\packages\GLPK\HjJiX\test\MOI_callbacks.jl:1
Test Summary: | Pass Error Broken Total
MathOptInterface | 1834 1 1 1836
Unit Tests | 782 782
Linear tests | 511 511
Linear Conic tests | 135 135
Integer Linear tests | 75 75
ModelLike tests | 246 1 247
Parameter setting | 4 4
Issue #79 | 2 2
Issue #70 | 6 6
Infeasible bounds | 1 1
RawParameter | 15 15
TimeLimitSec issue #110 | 4 4
RelativeGap | 2 2
Extra name tests | 15 15
Issue #102 | 2 2
Issue #116 | 3 3
Default parameters | 4 4
Duplicate names | 20 20
Duals with equal bounds | 2 2
PR #121 | 3 3
Non-ascii names | 2 2
ERROR: LoadError: Some tests did not pass: 1834 passed, 0 failed, 1 errored, 1 broken.
in expression starting at C:\Users\espenhs\.julia\packages\GLPK\HjJiX\test\runtests.jl:20
ERROR: Package GLPK errored during testing```
````
---
### Author:  [@Libbum](https://discourse.julialang.org/u/Libbum)
#### Post date: [January 31, 2020, 12:59pm UTC](https://discourse.julialang.org/t/lazyconstraint-not-defined-using-glpk-solver-callbacks/34012/2 "2020-01-31T12:59:21Z")
[Generic callbacks were dropped](https://github.com/JuliaOpt/JuMP.jl/issues/1553), so the example you’re using is out of date.
I’ll take a little deeper look to see if I can provide an alternate solution.
**Update:** [Maybe not anymore](https://github.com/JuliaOpt/JuMP.jl/pull/2101)
**2nd Update:** Looks like there is an [example](https://github.com/JuliaOpt/JuMP.jl/blob/dd68f8107339b15b41be147d6454202530606a3f/examples/callbacks.jl#L21-L46) for you in the current master branch of JuMP.
---
### Author:  [@odow](https://discourse.julialang.org/u/odow)
#### Post date: [January 31, 2020, 2:19pm UTC](https://discourse.julialang.org/t/lazyconstraint-not-defined-using-glpk-solver-callbacks/34012/3 "2020-01-31T14:19:58Z")
Yes, callbacks will be part of the next release of JuMP. You can use `] add JuMP#master` if you want to try them out before then!
Note that the documentation you linked to is out-of-date. Here’s the current documentation: [Introduction · JuMP](https://www.juliaopt.org/JuMP.jl/stable/)
I have a PR to fix the failing tests: [https://github.com/JuliaOpt/GLPK.jl/pull/127](https://github.com/JuliaOpt/GLPK.jl/pull/127)
---
### Author:  [@Espenol](https://discourse.julialang.org/u/Espenol)
#### Post date: [February 10, 2020, 12:26pm UTC](https://discourse.julialang.org/t/lazyconstraint-not-defined-using-glpk-solver-callbacks/34012/4 "2020-02-10T12:26:49Z")
Thank you for your responses, they were super helpful! I have gotten the example to run, but my own code does not seem to want to run the callback function. The test for lazy\_called fails, as the callback function is never called. I thus have to ask, is there any special condition that must be fulfilled for callback function to be called? My interpretation is that it should be always called after a call to `optimize!`, as we then may wish to add extra constraints to the solution. The JuMP callback example in the master branch seems to do it this way as far as I can see, where multiple conditions are checked manually to see if new constraints should be added to the solution.
My actual code somewhat complex but I have not been able to break it down to a level where I can make callbacks run successfully. My code is like so (pretty much exactly like the example [found here](https://github.com/JuliaOpt/JuMP.jl/blob/master/examples/callbacks.jl) of which you are the author @odow , but it still does not run the callbacks):
```julia
using JuMP # JuMP v.0.20.3, aka the master branch as of 2020-02.07 (and not the latest release)
using GLPK
using Random
using Test
function foo()
# Prepare JuMP model
model = Model(GLPK.Optimizer)
@variable(model, 0 <=pgen1 <= 100)
@variable(model, 0 <=pgen2 <= 100)
#@constraint(m, pgen1+pgen2==100)
@objective(model, Max, 5*pgen1+1.2*pgen2)
lazy_called = false
function my_callback_function(cb_data) # callback for preventive constraints
lazy_called = true
print("Entered callback function. ")
TOL = 1e-6
con = @build_constraint(pgen1 <= 80)
MOI.submit(model, MOI.LazyConstraint(cb_data), con)
end
# Set lazy constraint, run optimization and perform tests
MOI.set(model, MOI.LazyConstraintCallback(), my_callback_function)
optimize!(model)
@test termination_status(model) == MOI.OPTIMAL
@test primal_status(model) == MOI.FEASIBLE_POINT
@test lazy_called
end
foo()
```
---
### Author:  [@miles.lubin](https://discourse.julialang.org/u/miles.lubin)
#### Post date: [February 10, 2020, 1:51pm UTC](https://discourse.julialang.org/t/lazyconstraint-not-defined-using-glpk-solver-callbacks/34012/5 "2020-02-10T13:51:22Z")
> [@Espenol](#):
>
> I thus have to ask, is there any special condition that must be fulfilled for callback function to be called?
Yes, integer or binary variables must be present in the model. The lazy constraint callback modifies a branch-and-bound procedure. If all variables are continuous, branch-and-bound won’t run, hence the callback will not be called.