Set parameters to Gurobi

Specific Domains Optimization (Mathematical)
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1

Hello,

I use Gurobi 9.1.2; Julia 1.6.2 and these packages:
Gurobi v0.9.14
JuMP v0.21.10

(I’ve seen that the C API has changed)

I try to tell Gurobi to use a specific optimizer (the PRIMAL (simplex) one):

LP_model = direct_model(Gurobi.Optimizer())

...

grb_model = backend(LP_model)
grb_env = GRBgetenv(grb_model)
@assert GRBsetintparam(grb_env, GRB_INT_PAR_METHOD, GRB_METHOD_PRIMAL) == 0 "Gurobi GRBsetintparam C call failed"
valueP = Ref{Cint}(1234)
@assert GRBgetintparam(grb_env, GRB_INT_PAR_METHOD, valueP) == 0 "Gurobi GRBgetintparam C call failed"
@assert valueP[] == GRB_METHOD_PRIMAL "Method was not set"

optimize!(LP_model)

This code doesn’t produce any error but when I do println(solution_summary(LP_model, verbose=true)), I get:

* Work counters
  Solve time (sec)   : 0.00157
  Simplex iterations : 0
  Barrier iterations : 53
  Node count         : 0

… from which I conclude Gurobi has used a Barrier method and not the Simplex one…

Am I using the JuMP C interface correctly ?

Note I’m a beginner here, so maybe I just don’t get how Gurobi works.

Thanks

2

It’s strange, I do this:

println(solution_summary(LP_model, verbose=true))
println("Simplex iterations : $(simplex_iterations(LP_model))")
println("Barrier iterations : $(barrier_iterations(LP_model))")

and I get this:

* Work counters
  Solve time (sec)   : 0.00164
  Simplex iterations : 0
  Barrier iterations : 37
  Node count         : 0

Simplex iterations : 37.0
Barrier iterations : 0

So the reported numbers seems swapped… Any idea ?

3

Use set_optimizer_attribute

using JuMP, Gurobi
model = Model(Gurobi.Optimizer)
set_optimizer_attribute(model, "Method", 0)

The Gurobi docs explain what the values are: https://www.gurobi.com/documentation/9.1/refman/method.html

The solution summary thing is fixed in the next release of JuMP. The numbers are just swapped in v0.21.

1 Like
4

Thanks for answering. I didn’t see the set_optimizer_attribute method. I was driven to more complex stuff by Google :slight_smile: I understand there’s a Gurobi documentation for many languages binding, but not for Julia.

5

Yes, Gurobi.jl is maintained by the community and is not an official product. Please tell Gurobi you are interested in official support for Julia.