Design of Computer Experiments for Optimization, Estimation of Function   Contours, and Related Objectives
  A computer code or simulator is a mathematical representation of a physical system, for example a set of differential equations. Running the code with given values of the vector of inputs, x, leads to an output y(x) or several such outputs. For instance, one application we use for illustration simulates the average tidal power, y, generated as a function of the turbine location, x = (x1, x2), in the Bay of Fundy, Nova Scotia, Canada (Ranjan et al. 2011). Performing scientific or engineering experiments via such a computer code is often more time and cost effective than running a physical experiment.   Choosing new runs sequentially for optimization, moving y to a target, etc. has been formalized using the concept of expected improvement (Jones et al. 1998). The next experimental run is made where the expected improvement in the function of interest is largest. This expectation is with respect to the predictive distribution of y from a statistical model relating y to x. By considering a set of possible inputs x for the new run, we can choose that which gives the largest expectation. 
Derek Bingham, Pritam Ranjan, William Welch
stat.ME