# Differences and similarities between nonnegative PCA and nonnegative matrix factorization

I have seen references in the literature to nonnegative principal component analysis (nPCA) and nonnegative matrix factorization (NMF). I have tried reading the papers on both of them but it is not clear to me what the differences and similarities between them are. By similarity, I mean I am also interested in knowing when the nPCA and NMF method will give the same solution. Can someone clarify this?