This paper is concerned with the nonnegativity preserving interpolation of data on rectangular grids. The function is a kind of bivariate rational interpolation spline with parameters, which is in the whole interpolation region. Sufficient conditions are derived on coefficients in the rational spline to ensure that the surfaces are always nonnegative if the original data are nonnegative. The gradients at the data sites are modified if necessary to ensure that the nonnegativity conditions are fulfilled. Some numerical examples are illustrated in the end of this paper.
Xingxuan Peng. Zhihong Li. Qian Sun. "Nonnegativity Preserving Interpolation by Bivariate Rational Spline Surface." J. Appl. Math. 2012 1 - 11, 2012. https://doi.org/10.1155/2012/624978