Generative Support Generation over Empty Sets

[pulsipher]

Currently, we get nasty errors if we have generative supports that don't need to generate anything.

Consider the case with FEGaussLobatto and num_nodes = 2:

using InfiniteOpt

model = InfiniteModel()
@infinite_parameter(model, t in [0, 1], num_supports = 3)
@variable(model, y, Infinite(t))
@objective(model, Min, integral(y, eval_method = FEGaussLobatto(), num_nodes = 2, t))
ERROR: ArgumentError: reducing over an empty collection is not allowed
Stacktrace:
  [1] _empty_reduce_error()
    @ Base .\reduce.jl:301
  [2] reduce_empty(op::Function, #unused#::Type{Float64})
    @ Base .\reduce.jl:311
  [3] mapreduce_empty(#unused#::typeof(identity), op::Function, T::Type)
    @ Base .\reduce.jl:345
  [4] reduce_empty(op::Base.MappingRF{typeof(identity), typeof(min)}, #unused#::Type{Float64})
    @ Base .\reduce.jl:331
  [5] reduce_empty_iter
    @ .\reduce.jl:357 [inlined]
  [6] mapreduce_empty_iter(f::Function, op::Function, itr::Vector{Float64}, ItrEltype::Base.HasEltype)
    @ Base .\reduce.jl:353
  [7] _mapreduce(f::typeof(identity), op::typeof(min), #unused#::IndexLinear, A::Vector{Float64})
    @ Base .\reduce.jl:402
  [8] _mapreduce_dim
    @ .\reducedim.jl:330 [inlined]
  [9] #mapreduce#725
    @ .\reducedim.jl:322 [inlined]
 [10] mapreduce
    @ .\reducedim.jl:322 [inlined]
 [11] #_minimum#747
    @ .\reducedim.jl:894 [inlined]
 [12] _minimum
    @ .\reducedim.jl:894 [inlined]
 [13] #_minimum#746
    @ .\reducedim.jl:893 [inlined]
 [14] _minimum
    @ .\reducedim.jl:893 [inlined]
 [15] #minimum#744
    @ .\reducedim.jl:889 [inlined]
 [16] minimum
    @ .\reducedim.jl:889 [inlined]
 [17] UniformGenerativeInfo(basis::Vector{Float64}, label::DataType, lb::Int64, ub::Int64)
    @ InfiniteOpt C:\Users\bbgui\Documents\InfiniteOpt.jl\src\datatypes.jl:337
 [18] generate_integral_data(pref::GeneralVariableRef, lower_bound::Float64, upper_bound::Float64, method::FEGaussLobatto; num_nodes::Int64, weight_func::Function)
    @ InfiniteOpt.MeasureToolbox C:\Users\bbgui\Documents\InfiniteOpt.jl\src\MeasureToolbox\integrals.jl:399
 [19] integral(expr::GeneralVariableRef, pref::GeneralVariableRef, lower_bound::Float64, upper_bound::Float64; kwargs::Base.Pairs{Symbol, Any, Tuple{Symbol, Symbol}, NamedTuple{(:eval_method, :num_nodes), Tuple{FEGaussLobatto, Int64}}})
    @ InfiniteOpt.MeasureToolbox C:\Users\bbgui\Documents\InfiniteOpt.jl\src\MeasureToolbox\integrals.jl:828
 [20] macro expansion
    @ C:\Users\bbgui\.julia\packages\MutableArithmetics\geMUn\src\rewrite.jl:322 [inlined]
 [21] macro expansion
    @ C:\Users\bbgui\.julia\packages\JuMP\9CBpS\src\macros.jl:1297 [inlined]
 [22] top-level scope
    @ REPL[174]:1