Re: Question about Homework 2 on document coordinates in LSI space

[[Folks--please make sure that you are not looking at hidden slides--as these may have inconsistencies and incomplete statements]

SVD gives

d-t = d-f * f-f * t-f'

the new coordinates of the docs are d-f * f-f

I pointed this out in the class when doing the main animated slide.. (I think you and the student are looking at some hidden slides which may have been left over there from long back--I did all my discussion in terms of d-f * f-f * t-f' and not in terms of
u sigma and v!)

rao

On Mon, Oct 6, 2008 at 1:51 PM, Garrett Wolf <garrett.wolf@asu.edu> wrote:

Rao I've had two students ask me this question today, and after looking through the slides I wasn't clear which they should be using for the homework as both were mentioned in the slides (one seemed to be marked as the one to use, but I just wanted to check to be sure).

Garrett

---------- Forwarded message ----------
From: Jianhui Chen <jchen74@asu.edu>
Date: Mon, Oct 6, 2008 at 1:48 PM
Subject: Question about Homework 2
To: Garrett.Wolf@asu.edu

Hi, Garrett,

I am a student in Dr. Rao's information retrieval class. I have a question regarding the homework.

In LSI, assume X is the doc-term matrix and denote its SVD by X = U \Sigma V'.

Should we use "U \Sigma" as the new documents representation or only "U" as the new documents

representation?

Seems both approaches are mentioned in Dr. Rao's slides. And in the homework, we need to use

the new documents representation to compute the similarity and plot the documents.

Please help to advice. Thanks.

Jianhui