Wednesday, April 2, 2014

Lecture 3 & Lab 1


- I thought about the discussion on the Karp+ algorithm. An update rule that works is:

   if x is in K then count[x]++
   else {
        if |K | = k then
               for all a in K do {
                   if count[a] = 0 then delete a from K & count
        if |K| <  k { insert x in K , set count[x] := 1; }

Note that x will not be inserted if sketch is full and no empty place appears after discounting. The proof works now. Intuitively, x may not get in this time, but does its job of discounting k symbols; so if it is frequent it will eventually make it into K when an infrequent element gets to 0 count.

- About the lab: for credit, hand me a short report (2 pages max) with your results. No code fragments, no screenshots please. I said within 2 weeks but it's easter break, so let's say for the 23rd.

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