Regarding M in homework question 2..

[Subbarao Kambhampati <rao@asu.edu>]

 Some of you (including the guy who asked a question at the beginning of 
the class today) seem to be confused by the  summation in the denominator 
of the weight values (page 2 of homework question 2).

 The summation goes from 0 to M-1, where M is the total number of unique 
terms
in all the documents combined.

  The confusion seems to be that how am I going to do the summation when I 
don't know the value of M.

 Basically, notice that this summation is equivalent to doing the 
summation just over the terms that do occur in the document (because for 
the rest of the terms, tf will be zero, making the contribution from that 
term to the sum zero)

Hope this helps

Rao