@article {IOPORT.03706249,
    author       = {Himmelblau, D.M. and Lindsay, J.W.},
    title        = {An evaluation of subsitute methods for derivatives in unconstrained optimization.},
    year         = {1980},
    journal      = {Operations Research},
    volume       = {28},
    issn         = {0030-364X},
    pages        = {668-686},
    publisher    = {INFORMS, Hanover, MD},
    doi          = {10.1287/opre.28.3.668},
    identifier   = {03706249},
}