Lecture 1 - Introduction

Lecture 1 - Introduction - 6.207/14.15: Networks Lecture 1:...

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Unformatted text preview: 6.207/14.15: Networks Lecture 1: Introduction Daron Acemoglu and Asu Ozdaglar MIT September 9, 2009 1 Networks: Lecture 1 Introduction Outline What are networks? Examples. Small worlds. Economic and social networks. Network effects. Networks as graphs. Strong triadic closure. Power in a network. Decisions and games in networks. Implications of strategic behavior. Rest of the course. Reading: EK, Chapter, 1 (also skim Chapters 3-5). Jackson, Chapter 1. 2 Networks: Lecture 1 Introduction Introduction What are networks? Why study networks? Which networks and which commonalities? Which tools? Networks are a representation of interaction structure among units. In the case of social and economic networks, these units ( nodes ) are individuals or firms. At some broad level, the study of networks can encompass the study of all kinds of interactions. Information transmission. Web links. Information exchange. Trade. Credit and financial flows. Friendship. Trust. Spread of epidemics. Diffusion of ideas and innovation. 3 Networks: Lecture 1 Introduction Visual Examples1 Figure: The network structure of political blogs prior to the 2004 U.S. Presidential election reveals two natural and well-separated clusters (Adamic and Glance, 2005) 4 Networks: Lecture 1 Introduction Visual Examples2 Figure: The social network of friendships within a 34-person karate club provides clues to the fault lines that eventually split the club apart (Zachary, 1977) 5 Networks: Lecture 1 Introduction Visual Examples3 Figure: The network of loans among financial institutions can be used to analyze the roles that different participants play in the financial system, and how the interactions among these roles affect the health of individual participants and the system as a whole. ( Bech and Atalay 2008) 6 Networks: Lecture 1 Introduction Visual Examples4 Figure: The web link structure centered at http://web.mit.edu (touchgraph) 7 Networks: Lecture 1 Introduction Visual Examples5 Figure: The spread of an epidemic disease (such as the tuberculosis outbreak shown here) is another form of cascading behavior in a network. The similarities and contrasts between biological and social contagion lead to interesting research questions. (Andre et al. 2007) 8 Networks: Lecture 1 Introduction Visual Examples6 Figure: When people are influenced by the behaviors of their neighbors in the network, the adoption of a new product or innovation can cascade through the network structure. Here, e-mail recommendations for a Japanese graphic novel spread in a kind of informational or social contagion. (Leskovec et al. 2007) 9 Networks: Lecture 1 Introduction Visual Examples7 Figure: Percentage of total corn acreage planted with hybrid seed. (USDA Agricultural Statistics) 10 Networks: Lecture 1 Introduction Do We Live in a Small World?...
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Lecture 1 - Introduction - 6.207/14.15: Networks Lecture 1:...

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