Chenxue Yang and  Mao Ye and  Zijian Liu and  Tao Li and  Jiao Bao,  Convergence Analysis of an Alternative Gradient Algorithm for Non-Negative Matrix Factorization.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    February 2014, vol. 85(1). 201 - 210
    [viewed 16 October 2019]. Available from: https://publications.waset.org/pdf/9997720.