SCIP.jl with exact-rational branch

[melkael]

Hello

I am trying to use the exact-rational branch of SCIP with this package. I managed to compile if fine to pass the install dir to SCIP.jl in my ENV[“SCIPOPTDIR”].

As indicated on the Readme of the branch (see https://github.com/scipopt/scip/tree/exact-rational), it is required to set the parameter exact/exact_enabled.

However, when I try to set the parameter with set_attribute(model, "exact/exact_enabled", "TRUE")

I obtain:

ERROR: LoadError: Unrecognized parameter: exact/exact_enabled
Stacktrace:
  [1] error(s::String)
    @ Base ./error.jl:35
  [2] set_parameter(scipd::SCIP.SCIPData, name::String, value::String)
    @ SCIP ~/.julia/packages/SCIP/S9mBb/src/scip_data.jl:123
  [3] set
    @ ~/.julia/packages/SCIP/S9mBb/src/MOI_wrapper.jl:179 [inlined]
  [4] set
    @ ~/.julia/packages/MathOptInterface/gBojA/src/Bridges/bridge_optimizer.jl:955 [inlined]
  [5] set(model::MathOptInterface.Utilities.CachingOptimizer{MathOptInterface.Bridges.LazyBridgeOptimizer{SCIP.Optimizer}, MathOptInterface.Utilities.UniversalFallback{MathOptInterface.Utilities.Model{Float64}}}, attr::MathOptInterface.RawOptimizerAttribute, value::String)
    @ MathOptInterface.Utilities ~/.julia/packages/MathOptInterface/gBojA/src/Utilities/cachingoptimizer.jl:1059
  [6] set(m::Model, attr::MathOptInterface.RawOptimizerAttribute, value::String)
    @ JuMP ~/.julia/packages/JuMP/as6Ji/src/optimizer_interface.jl:794
  [7] set_attribute
    @ ~/.julia/packages/JuMP/as6Ji/src/optimizer_interface.jl:1023 [inlined]
  [8] set_attribute
    @ ~/.julia/packages/JuMP/as6Ji/src/optimizer_interface.jl:1032 [inlined]
  [9] iabtree_throughput(G::MetaDiGraph{Int64, Float64}, json_comm::Vector{Any}, gap::Float64, continuous_ue_links::Bool, maxtime::Float64, scaling_caps::Int64)
    @ Main /home/IABEnergySavingJournal/solver/model.jl:70
 [10] macro expansion
    @ ./timing.jl:279 [inlined]
 [11] main(method::String, data::Dict{String, Any}, result_name::String)
    @ Main /home/IABEnergySavingJournal/solver/test_json.jl:75
 [12] top-level scope
    @ /home/IABEnergySavingJournal/solver/test_json.jl:107
in expression starting at /home/IABEnergySavingJournal/solver/test_json.jl:107

I also tried set_attribute(model, "exact/exact_enabled", true) and set_attribute(model, "exact/exact_enabled", 1) with the same outcome. I suspect I need to implement something regarding this parameter within SCIP.jl but am unsure what to change.

[matbesancon]

Hi, are you sure SCIP.jl is correctly linked to your SCIP installation? You can test that with:

@eval SCIP.libscip

which points to the path where the SCIP shared library is

[leoneifler]

Hi, sorry that is a typo in the documentation. The parameter ist 'exact/enabled'. Will fix this.

[melkael]

Thank you for your help, it now works with "exact/enabled". However, it seems like Julia initializes the problem creation when SCIP.Optimizer() is called, which prevents me from setting the exact mode. I get the following error:

[set.c:767] ERROR: Exact solving mode can only be enabled/disabled before reading/creating a problem.

[leoneifler]

Hmm, that is a bit of an issue. I don´t know what can be done on the Julia side of things. The reason this error is necessary is that reading a problem in inexact mode already might not give you exactly the problem you want to solve (inaccuracies when converting to binary, setting small values to 0, etc.)

As a hacky fix, you could just set the parameters default value to true in set.c (SCIP_DEFAULT_EXACT_ENABLED)

[melkael]

Sounds like a good solution, I will try that, thank you!

[matbesancon]

Closing for now, I don't think we have the bandwidth to support the exact mode from the Julia wrapper