# Question on allowing user to specify the optimization sense

**URL:** <https://discourse.julialang.org/t/question-on-allowing-user-to-specify-the-optimization-sense/84836>\
**Category:** Optimization (Mathematical)\
**Tags:** question, package, jump\
**Created:** [July 26, 2022, 5:31pm UTC](https://discourse.julialang.org/t/question-on-allowing-user-to-specify-the-optimization-sense/84836 "2022-07-26T17:31:36Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![math\_opt](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/math_opt/32/25317_2.png) [@math\_opt](https://discourse.julialang.org/u/math_opt)\
**Post date:** [July 26, 2022, 5:31pm UTC](https://discourse.julialang.org/t/question-on-allowing-user-to-specify-the-optimization-sense/84836/1 "2022-07-26T17:31:36Z")

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I have a small package in which I solve an optimization model. The `sense` of the objective function is to be specified by the user. Now, I export `MAX_SENSE` and `MIN_SENSE` for the user to use them. A small example:

```julia
module MyPkg

using JuMP
using Gurobi

export solve, MAX_SENSE, MIN_SENSE

function solve(sense::MOI.OptimizationSense)
    model = Model(Gurobi.Optimizer)
    @variable(model, x[1:2] >= 0)
    @constraint(model, sum(x) <= 2)
    @objective(model, sense, 2*x[1]+x[2])
    
    optimize!(model)
    if termination_status == MOI.OPTIMAL 
        return objective_valule(model)
    else
        error("Not solved to optimality")
    end
end

end

```

I have a couple of questions here:

1. Is there another (more safe, neat, and probably more standard) way to allow users to allow specifying the objective without exporting `MIN_SENSE` and `MAX_SENSE`. I want to keep the exported items to a minimum.
2. I haven’t explicitly added the following lines to my package:

```julia
using MathOptInterface
const MOI = MathOptInterface

```

However, I could still use `MOI.OptimizationSense` and `MOI.OPTIMAL` inside my package functions without any issue. So my question is, why is it working exactly? Also, I have seen some packages that actually add the lines mentioned above, so when do I actually need to add the `using MathOptInterface; const MOI = MathOptInterface` lines to my package?

1. How is `MOI.ObjectiveSense` related to the `MOI.OptimizationSense`? I can find the documentation for the former [here](https://jump.dev/MathOptInterface.jl/stable/reference/models/#MathOptInterface.ObjectiveSense), but nothing on the latter. Any reference or explanation about the difference between the two would be appreciated.

Thanks!

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<div class="post-metadata">

**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:** [July 26, 2022, 10:29pm UTC](https://discourse.julialang.org/t/question-on-allowing-user-to-specify-the-optimization-sense/84836/2 "2022-07-26T22:29:16Z")

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> [@math\_opt](#):
>
> Is there another (more safe, neat, and probably more standard) way to allow users to allow specifying the objective without exporting `MIN_SENSE` and `MAX_SENSE`. I want to keep the exported items to a minimum.

Use an argument like

```Julia
function solve(; maximize::Bool)
    sense = maximize ? MOI.MAX_SENSE : MOI.MIN_SENSE
    # ...
end

solve(; maximize = true)

```

> 1. I haven’t explicitly added the following lines to my package:

JuMP exports the `MOI` constant, so `using JuMP` pulls `MOI` into scope.

> 1. How is `MOI.ObjectiveSense` related to the `MOI.OptimizationSense` ?

`ObjectiveSense` is the attribute, as in `MOI.ObjectiveSense()`. `OptimizationSense` is the enum, as in `MOI.MIN_SENSE`.

```julia
help?> MOI.ObjectiveSense
  ObjectiveSense()

  A model attribute for the objective sense of the objective function, which must be an
  OptimizationSense: MIN_SENSE, MAX_SENSE, or FEASIBILITY_SENSE. The default is FEASIBILITY_SENSE.

  Interaction with ObjectiveFunction
  ====================================

  Setting the sense to FEASIBILITY_SENSE unsets the ObjectiveFunction attribute. That is, if you
  first set ObjectiveFunction and then set ObjectiveSense to be FEASIBILITY_SENSE, no objective
  function will be passed to the solver.

  In addition, some reformulations of ObjectiveFunction via bridges rely on the value of
  ObjectiveSense. Therefore, you should set ObjectiveSense before setting ObjectiveFunction.

julia> MOI.OptimizationSense
Enum MathOptInterface.OptimizationSense:
MIN_SENSE = 0
MAX_SENSE = 1
FEASIBILITY_SENSE = 2

```

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<div class="post-metadata">

**Author:** ![math\_opt](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/math_opt/32/25317_2.png) [@math\_opt](https://discourse.julialang.org/u/math_opt)\
**Post date:** [July 27, 2022, 2:53am UTC](https://discourse.julialang.org/t/question-on-allowing-user-to-specify-the-optimization-sense/84836/3 "2022-07-27T02:53:49Z")

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Amazing. That makes it much more clear. Thanks!