MethodError: reducing over an empty collection

[odow]

julia> using JuMP, EAGO

julia> begin
           model = Model(EAGO.Optimizer)
           @variable(model, x == 2)
           @variable(model, y == 3)
           @constraint(model, sqrt(x * y) <= 3)
           optimize!(model)
       end
ERROR: MethodError: reducing over an empty collection is not allowed; consider supplying `init` to the reducer
Stacktrace:
  [1] reduce_empty(op::Base.MappingRF{EAGO.var"#1#2"{EAGO.var"#134#135"{EAGO.GlobalOptimizer{…}}}, Base.BottomRF{typeof(EAGO._rf_findmax)}}, ::Type{Pair{Int64, Int64}})
    @ Base ./reduce.jl:361
  [2] reduce_empty_iter
    @ ./reduce.jl:384 [inlined]
  [3] reduce_empty_iter
    @ ./reduce.jl:383 [inlined]
  [4] foldl_impl
    @ ./reduce.jl:49 [inlined]
  [5] mapfoldl_impl
    @ ./reduce.jl:44 [inlined]
  [6] mapfoldl
    @ ./reduce.jl:175 [inlined]
  [7] map_findmax
    @ ~/.julia/packages/EAGO/oWEmA/src/eago_optimizer/utilities.jl:35 [inlined]
  [8] map_argmax
    @ ~/.julia/packages/EAGO/oWEmA/src/eago_optimizer/utilities.jl:36 [inlined]
  [9] _select_branch_variable_width
    @ ~/.julia/packages/EAGO/oWEmA/src/eago_optimizer/optimize/nonconvex/stack_management.jl:95 [inlined]
 [10] select_branch_variable
    @ ~/.julia/packages/EAGO/oWEmA/src/eago_optimizer/optimize/nonconvex/stack_management.jl:106 [inlined]
 [11] branch_node!(t::EAGO.DefaultExt, m::EAGO.GlobalOptimizer{EAGO.Incremental{Cbc.Optimizer}, EAGO.Incremental{Ipopt.Optimizer}, EAGO.DefaultExt})
    @ EAGO ~/.julia/packages/EAGO/oWEmA/src/eago_optimizer/optimize/nonconvex/stack_management.jl:137
 [12] branch_node!
    @ ~/.julia/packages/EAGO/oWEmA/src/eago_optimizer/optimize/nonconvex/stack_management.jl:179 [inlined]
 [13] global_solve!(m::EAGO.GlobalOptimizer{EAGO.Incremental{Cbc.Optimizer}, EAGO.Incremental{Ipopt.Optimizer}, EAGO.DefaultExt})
    @ EAGO ~/.julia/packages/EAGO/oWEmA/src/eago_optimizer/optimize/optimize_nonconvex.jl:425
 [14] optimize!
    @ ~/.julia/packages/EAGO/oWEmA/src/eago_optimizer/optimize/optimize_nonconvex.jl:493 [inlined]
 [15] optimize!(m::Optimizer{EAGO.Incremental{Cbc.Optimizer}, EAGO.Incremental{Ipopt.Optimizer}, EAGO.DefaultExt})
    @ EAGO ~/.julia/packages/EAGO/oWEmA/src/eago_optimizer/optimize/optimize.jl:40
 [16] optimize!
    @ ~/.julia/packages/MathOptInterface/gLl4d/src/Bridges/bridge_optimizer.jl:367 [inlined]
 [17] optimize!
    @ ~/.julia/packages/MathOptInterface/gLl4d/src/MathOptInterface.jl:122 [inlined]
 [18] optimize!(m::MathOptInterface.Utilities.CachingOptimizer{MathOptInterface.Bridges.LazyBridgeOptimizer{…}, MathOptInterface.Utilities.UniversalFallback{…}})
    @ MathOptInterface.Utilities ~/.julia/packages/MathOptInterface/gLl4d/src/Utilities/cachingoptimizer.jl:321
 [19] optimize!(model::Model; ignore_optimize_hook::Bool, _differentiation_backend::MathOptInterface.Nonlinear.SparseReverseMode, kwargs::@Kwargs{})
    @ JuMP ~/.julia/packages/JuMP/i68GU/src/optimizer_interface.jl:595
 [20] optimize!(model::Model)
    @ JuMP ~/.julia/packages/JuMP/i68GU/src/optimizer_interface.jl:546
 [21] top-level scope
    @ REPL[16]:6
Some type information was truncated. Use `show(err)` to see complete types.

(ipopt) pkg> st
Status `/private/tmp/ipopt/Project.toml`
  [bb8be931] EAGO v0.8.2
  [4076af6c] JuMP v1.23.5

[DimitriAlston]

This is because of EAGO's branch-and-bound routine that gets called when given a nonlinear problem. The variables are fixed so they are not labeled as branch variables, which returns this error. I will have to add some checks so that EAGO doesn't try to branch in a case like this. Thanks for pointing it out!