Gradient of the Scaling function (marginal in dimension k) of Xiong et al. with respect to eta
scalingGrad(X, knots, k)an n*d matrix standing for a design of n experiments in d-dimensional space.
a list of knots parametrizing the transformation.
dimension of the input variables for which the gradient is calculated.
Gradient of the Scaling function of Xiong et al. with respect to eta
Y. Xiong, W. Chen, D. Apley, and X. Ding (2007), Int. J. Numer. Meth. Engng, A non-stationary covariance-based Kriging method for metamodelling in engineering design.