Archives for the month of: June, 2013

LSI, LSA, pLSA, LDA, etc

•What is the difference between LSI and LSA?
–LSI refers to using this technique for indexing, or information retrieval.
–LSA refers to using it for everything else.
–It’s the same technique, just different applications.


•Two problems that arise using the vector space model:
–synonymy: many ways to refer to the same object, e.g. car and automobile
•leads to poor recall
–polysemy: most words have more than one distinct meaning, e.g. model, python, chip
•leads to poor precision

PCA with standardization in Matlab

By running [coeff,score,latent] = pca(X, ‘Centered’, true, ‘VariableWeights’, ‘variance’);, we can get the standardized PCA results. (The transformed observations are in score.)

When running just [coeff,score,latent] = pca(X);, only centering is applied.