S. Sakata F. Ashida M. Zako Comparative study on gradient and Hessian estimation using the Kriging method and neural network approximation. 309-319 2010 51 Mathematical and Computer Modelling 3-4 http://dx.doi.org/10.1016/j.mcm.2009.08.016 db/journals/mcm/mcm51.html#SakataAZ10