SVD is used in LSA to get the latent semantic information. I am confused about the interpretation about the SVD matrices.
We first build a document-term matrix. And then use SVD to decompose it into 3 matrices.
For example:
The doc-term matrix M1 is M x N, where:
M = the number of documents
N = the number of terms
And M1 was decomposed into:
M1 = M2 * M3 * M4, where:
M2: M x k
M3: k x k
M4: k x N
I see the interpretation like below:
The k column of M2 stands for categories of similar semantics. The k row of M4 stands for the topics.
My questions are:
Why is k interpreted like above? How do we know it is similar semantics and topics?
Why the similar semantics equal the topics?
Why k is interpreted differently between M2 and M4
How to interpret the M3?
I am really confused. It seems the interpretation is totally arbitrary. Is that what latent meant to be?
I warmly recommend reading the information retrieval chapter in the SNLP bible by Manning and Schutze. In 5 pages it explains everything you want to know about LSI and SVD.
You will find paragraphs like this :