Non-negative matrix factorization (NMF or NNMF), also non-negative matrix approximation[1][2] is a group of algorithms in multivariate analysis and linear algebra where a matrixV is factorized into (usually) two matrices W and H, with the property that all three matrices have no negative elements. This non-negativity makes the resulting matrices easier to inspect. Also, in applications such as processing of audio spectrograms or muscular activity, non-negativity is inherent to the data being considered. Since the problem is not exactly solvable in general, it is commonly approximated numerically.
^Rainer Gemulla; Erik Nijkamp; Peter J. Haas; Yannis Sismanis (2011). Large-scale matrix factorization with distributed stochastic gradient descent. Proc. ACM SIGKDD Int'l Conf. on Knowledge discovery and data mining. pp. 69–77.