PCA Is Not LSI

The fact that singular value decomposition (SVD) is used in principal component analysis (PCA) and in latent semantic indexing (LSI) has made some (even some “johnnycomeslate-to-IR” assistant professors) to think that PCA is LSI.

On SVD and PCA: Some Applications

Some readers have asked me to clarify the difference between SVD and PCA, since these have many overlapping heritages. This was clarified at a TREC9 presentation. For those interested in a mathematical explanation or in ongoing research using these, the following might help.