Qian, Shixian et F. Eddy, William, An algorithm for isotonic regression on ordered rectangular grids, Journal of computational and graphical statistics , 5(3), 1996, pp. 225-235
In this article, we give an algorithm for isotonic regressions on ordered rectangular grids. The running time of the algorithm is no more than cubic in the number of grid points. This algorithm makes bivariate isotonic regression a practical choice for some data analysis.