I'm trying to learn about the geometric interpretation of NMF. I have found the paper by Slim Essid to be very useful. I would like to make a plot like the one in Figure 1 just for a k=2 Topics (i.e. the 2d case). What are the axes in Figure 1. Thanks for your help.
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The axes are literally dimensions in the feature space. Vectors inside are data points. Vectors between the data and the positive axes are the "topics". I think Page 22--24 (especially Figure 3.1) of Gillis' thesis (https://www.dropbox.com/s/dyfusffzymewoim/Thesis_gillis.pdf?dl=0) should be helpful for the precise definition of these things. Sec 3 of https://www.stanford.edu/~vcs/papers/NMFCDP.pdf is also very clear about the geometric interpretation of NMF (it is probably where it first appeared).
