Make a RootProblem type

[dpsanders]

It may be useful to have a RootProblem type that encodes the function, the IntervalBox, the dimension, etc.

[dpsanders]

Here's a possible definition for a type to wrap a function:

"""
Type representing a function to be used in a branch and bound algorithm
"""

struct BranchAndBoundFunction{F,N,T}
    f::F
    X::IntervalBox{N,T}
    input_dim::Int
    output_dim::Int

    function BranchAndBoundFunction(f::F, X::IntervalBox{N,T}) where {F<:Function,N,T}
        new{F,N,T}(f, X, N, length(f(X)))
    end
end

(f::BranchAndBoundFunction{F,N,T})(X::IntervalBox{N,T}) where {F,N,T} = f.f(X)