I would like to know (if possible) how does one find exact the non-negative matrix factorization ($AW$) of a given matrix $M$ of a small size?
I know the problem is NP-hard. The method I know is by Fixing $A$ then optimize and modify $W$, then fix $W$, optimize, repeat... but is there a way to do it manually (on paper) for small matrices ( $3\times4$ or a $4\times5$ matrix) ?