Non-negative matrix factorization (NMF) has been shown to be a useful decomposition for multivariate data in recent decades. In this study, we will focus on the numerical algorithm for NMF which is recast as the problem of approximating a polytope on the probability simplex by another polytope with fewer facets. Chu and Lin [1] proposed an algorithm for computing the proximity map which is more convenient to nd the unique global minimum per iteration than the existing methods. Nevertheless, their method is less competitive in speed with other methods though one could have much smaller residual errors in factorization. To improve the eciency of Chu-Lin method, we program the algorithm by C language, which successfully speeds up the computation than the one given in [1]. We also compare the computational cost for di erent settings of matrices dimensions.