This defines abstract method type and implements functions for abstract mehtod.

This calls function BundleModel.evaluate_f(y) to get function value fy and gradient g. This method assumes user-defined function of the form evaluate_f(y::Vector{Float64})::Tuple{Float64,Array{Float64,2}} returning function evaluation value and gradient as first and second outputs, resp.

This calls function BundleModel.evaluate_f(y) to get function value fy and gradient g. This method assumes user-defined function of the form evaluate_f(y::Vector{Float64})::Tuple{Float64,Array{Float64,2}} returning function evaluation value and gradient as first and second outputs, resp.