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## 2018 Q15

Hello,

I am really confused about for the first choice, why there is only one solution?

Thank you very much for your help!!!

## 2

Hi, I think that it is not meant unique solution for W and Z, but that there exist W and Z such that X = WZ^T (where X is a matrix that we want to factorize). If K < min{N, D}, than X not necessarily equals WZ^T, but it is just nicely approximated with it.

## 3

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