Response surface approximation using gradient information

† Institute of Mechanical Engineering, Aalborg University, Aalborg, Denmark. e-mail: stl@ime.auc.dk ‡ Department of Aerospace Engineering, Mechanics and Engineering Sciences, University of Florida, Gainesville, FL, USA. e-mail: vitali@ufl.edu & haftka@aero.ufl.edu § Technische Universitat Delft, Delft, The Netherlands. email: F.vanKeulen@wbmt.tudelft.nl ¶ Vanderplaats R&D, Colorado Springs, CO, USA, email: jens@vrand.com