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Unformatted text preview: Networks: Fall 2010 Homework 1 David Easley and Jon Kleinberg Due by start of class, September 8, 2010 As noted on the course home page, homework solutions must be submitted by upload to the CMS site, at https://cms.csuglab.cornell.edu/ . This means that you should write these up in an electronic format (Word files, PDF files, and most other formats can be uploaded to CMS). Homework will be due at the start of class on the due date, and the CMS site will stop accepting homework uploads after this point. We cannot accept late homework except for University-approved excuses (which include illness, a family emergency, or travel as part of a University sports team or other University activity). Reading: The questions below are primarily based on the material in Chapters 2, 3, and 5 of the book. (1) (This is Exercise 3 from Chapter 3.) In the social network depicted in Figure 1, with each edge labeled as either a strong or weak tie, which nodes violate the Strong Triadic Closure Property from Chapter 3, and which satisfy it? (Recall that unless a node violates the property, following the definition from the book, it is said to satisfy it.) Provide an explanation for your answer. A B D C E S S S W S S W W Figure 1: (2) Suppose that youre working with a group of sociologists who are studying the friend- ships among students at a boarding school. Students live at this school from the ages of 8 1 to whom X is not currently connected, but who X might want to connect to. If Y is chosen by the system as the recommendation for X , then X receives a prompt on his/her screen asking if X would like to add Y as a friend. The recommendation is viewed as successful if X accepts the suggestion and adds Y . Youve been attending meetings in which the team in charge of the recommendation system shows the results of the system on various real-life examples, and then you suggest whether you think the system made the right recommendation. In this way, the recommen- dation team can try identifying deficiencies in their methods. (a) In one example, the team shows you Figure 2, consisting of the user X and all nodes in the system who are at a distance of either 1 or 2 from X in the social network. In this example, the system recommended user A to X . Do you think this was the best choice? If so, explain why; if not, say what you think would be a better choice, and again explain why. In either case, relate your explanation to principles from class. (b) Currently the recommendation system is based on looking at small portions of the social network like the one in Figure 2. The recommendation team asks whether you think it would be useful to incorporate other forms of information in deciding which node to recom- mend to X . (Although the current recommendation system is only using nodes and edges, as in the figure, the social-networking system itself is recording all the actions taken by all its users, with time-stamps on all these actions, so there are many sources of information...
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This note was uploaded on 11/11/2010 for the course ECON 2040 taught by Professor Easley/kleinberg during the Fall '07 term at Cornell University (Engineering School).
- Fall '07