LSA stands for [Latent Semantic Analysis](https://en.wikipedia.org/wiki/Latent_semantic_analysis), a natural language processing technique which involves analysing the relationships between documents and terms they contain by producing a set of related concepts.
1
vote
0answers
40 views
Is that overfitting?
Given a document-term matrix $X$, where $$X(d, t) = \textit{occurrences of 't' in 'd'}$$, it's possible to compute it's Truncated Singular Value Decomposition:$$X_k = U_k \Sigma_k V_k^T$$
Then, for a ...
0
votes
0answers
34 views
Improve LSA perfomances using weighting schemes (tf-idf)
In the context Natural Language Processing, weighting the matrix of terms occurences with a schema based on term-frequency (tf) and inverse-document-frequency (idf), also known as tf-idf schemes, can ...
0
votes
0answers
48 views
What are the similarities between ICA and LSA in machine learning?
I couldn't find much information on the main similarities between Independent Component Analysis and Latent Semantic Analysis.
Does anyone know the key similarity / similarities?
2
votes
1answer
196 views
A parellel between LSA and pLSA
In the original paper of pLSA the author, Thomas Hoffman, draw a parallel between pLSA and LSA data structures that I would like to discuss with you.
Background:
Taking inspiration the Information ...
1
vote
2answers
85 views
Derivation of M-step for pLSA
I was looking at section 6 of these notes and trying to understand the derivation of the M-step at the top of page 10. I understood the derivation for the model without background, but I do not ...
2
votes
0answers
32 views
Initialization in pLSA
I'm using pLSA (Probabilistic Latent Semantic Analysis). I'm trying to estimate the best value for some parameters with a process of k-fold cross-validation.
I have noticed that the model fitting is ...
2
votes
0answers
475 views
How to cluster LDA/LSI topics generated by gensim?
I'm an enthusiastic single developer working on a small start-up idea. I reduced a corpus of mine to an LSA/LDA vector space using gensim. Now I have a bunch of ...
8
votes
3answers
228 views
Fast alternatives to the EM algorithm
Are there any speedy alternatives to the EM algorithm for learning models with latent variables (especially pLSA)? I'm okay with sacrificing precision in favor of speed.
1
vote
1answer
64 views
Is there a sequential version of probabilistic latent semantic analysis?
Does someone know if it exists some way to do online learning with pLSA? The model training is really time consuming, so it is not feasible to rebuild it after every changes in the data.
3
votes
0answers
85 views
Finding similarity between a reference and few working documents
I have to find the similarity between a reference document and a set of documents in a repository .
Here is my method :
...
0
votes
0answers
175 views
Can LSA be used for document similarity?
I have to find the similarity between two documents. The two documents are simple text documents and i have to report a score. I was using cosine similarity initially. But I was told that LSA is a ...
1
vote
1answer
475 views
When to choose PCA vs. LSA/LSI
Question:
Are there any general guidelines with respect to the input data characteristics, that can be used to decide between applying PCA versus LSA/LSI?
Brief summary of PCA vs. LSA/LSI:
...
0
votes
1answer
164 views
pLSA - Probabilistic Latent Semantic Analysis, how to choose topic number?
I am approaching to pLSA (Probabilistic Latent Semantic Analysis) in this period, to apply it to biomolecular annotation prediction.
A very simple question: how to choose the number of topics/classes ...
3
votes
1answer
333 views
What is a “tempered EM algorithm”?
In the paper of Probabilistic Latent Semantic Analysis by Hofmann, the author fits the model for document $\times$ word matrix through EM Algorithm in section 3. I was able to follow the derivation ...
1
vote
1answer
236 views
Derivation of E step in EM algorithm
While im going through the derivation of E step in EM algorithm for pLSA, i came across the following derivation at this page. Could anyone explain me how the following step is derived.
$\sum_z q(z) ...
5
votes
2answers
317 views
Deriving mathematical model of pLSA
After knowing how LSA works, I went on continue reading on pLSA but couldn't really make sense of the mathematical formula. This is what I get from wikipedia (other academic papers/tutorial show ...
