## Tuesday, September 2, 2008

### added two more questions to homework 1

ntv1534 said...

I must be misunderstanding #7, because it doesn't seem to make sense...or I've forgotten my linear algebra.

"7. Let one of the eigen vectors you computed in part 5 be v, and the correspondng eigen value l. "
<- that l looks like a 1, which may confuse a student the first time through

"Compute AXv (where X is the matrix multiplication of A with v). Show that AXv is actually l*v (that is multiptlying the eigen vector with A only increases its size)."

If A is the given 2x2 matrix, and v is the eigenvector (which, unless I'm crazy, is 2x1), then X is 2x1. Since matrix multiplication requires the inner dimensions to be the same, I'm not sure how to do Xv ...considering part 8 uses the same multiplication I'm sure it must be valid...am I forgetting something fundamental?

Pierre said...

I think that "X" is the multiplication operator, and not a variable.

Raju said...

Vijayakrishnan, Here you assume that only the query is stemmed, and document is not. But you use the same stemming algorithm on queries and documents.

ntv1534 said...

(>_<)...that does, in fact, make much more sense. Thanks pierre!

Nick Vaidyanathan said...
This comment has been removed by the author.
Shashvata said...

For Question 3:

The values in the tf-idf document-term matrix given in the slides seem to be incorrect for documnets d6-d10.

For sub-question 4, I think we'll have to calculate the correct values for d6 and d8.