Monday, January 3, 2011

Homework 1

Homework 1 was passed out in class today, and is available on the course website.

Note that there is a typo in the due date on the ones handed out in class -- it is due next Thursday, Jan 13 at 1:30pm.  Be sure to start early.

Also, if you're nervous about whether you know enough probability, try out the first two problems and attend Raga's Probability refresher on Friday if you have any trouble.

If you have any questions about the homework (or want to point out typos), write a comments on this post and  the TAs/prof will respond ASAP.


  1. Some of you have apparently started already!

    I just got this question via email:

    "Is there an easy way to look through co-authorship for the final problem? Everything else in the 6 degrees of freedom problem has an easy way to jump through the links but is there a way to do this with co-authorship? "

    Here's my response:

    Yes, there's an easy way, you just have to find the right tool...

    If you use the advanced options, google scholar makes this doable...but there are other tools that you can find that make it even easier.

    Part of the goal of asking the question is for you to have to explore what people are doing with "coauthor networks" enough to find the right tool :)

  2. For problem 1b, are the graph's edges weighted or unweighted?

  3. It is possible to come up with an unweighted graph for 1b, so weights are not really necessary. You could use weights if you like.

  4. When computing the average distance for 1b, because the graph is undirected do we count the path distance only once? So we only count from node a to node b and not vis versa? Also, do we include the path from a node to itself of distance 0 in doing the average distance?

  5. To compute the average distance, you average the distance between any two distinct nodes (if you count each pair twice, you will also have counted the distance between them twice, so it doesn't matter).

  6. For the 6 degrees of separation problem, I noticed that the "customers also bought" links on amazon tend to change from day to day. And the pages for these recommendations start to shift. I was verifying my solution and I noticed the page numbers started moving backward from what I had recorded them initially as. I'm worried that a solution I have now will no longer work later. How will this be handled?

  7. For the amazon question, write down the shortest path that you found along with the date on which you found it.

  8. For the Amazon question part b...
    Do you want us to start from

    "Dove cool moisture beauty bar, 14 count" or
    "Dove cool moisture beauty bar, 25.5 oz"

    I don't think there is a page that just states

    "Dove cool moisture beauty bar"

    by the way... this question sounds too funny...

  9. The starting point is "Dove cool moisture beauty bar, 14 count." And I'm glad you found it funny.

  10. For 2b, is a loop defined only as when a single rope's two ends are tied together?

    Or can a loop also be when N ropes are tied together to form a loop?

  11. The second one is correct. A loop can be formed with more than one rope.

  12. @Everyone from the TA: If you have any queries regarding HW1, feel free to drop in on Thursday from 9:00am to 12:00 noon at Annenberg 232. I can help you if you have any queries remaining.