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kb0000 (9) [Avatar] Offline
I am confused by the discussion of how to get the matrix factor V. If I highlight just the salient points of the paragraph, the discussion appears to say this:

The last matrix factor, V, ... is the "answer", the topic vector...but we also want to be able to compute it on a new bag of words or TF-IDF vector...we can compute it anew whenever we need it. To create a row in this matrix we multiply the inverse of the V matrix by any new TF-IDF vector...

That is, it appears to say that we do not need to retain the V matrix but can recreate it on demand by...multiplying the inverse of the V matrix by any new vector? If we are trying to calculate the V matrix I'm not sure how exactly we can take its inverse before we calculate it. Undoubtedly this is described in many other resources but this seemed to be a section where you wanted to make the discussion self contained.
hobs (58) [Avatar] Offline
You are right. We didn't do a good job explaining it because I didn't fully understand it at the time. I think it's a little better now.