about non negative matrix factorization

what is N*M in D = norm(A-W*H,'fro')/sqrt(N*M)? This has never been mentioned before. and i know nnmf muliplicative algorithm does not change initial value. when I use that code like second picture i guess W1 must be fixed stdW , but it changed

please tell me why.

Answer 1

[Jan]

According to your screenshot, the function operates on an "n by m matrix". Then I'm convinced that "N*M" is the number of elements.