In the following, please include an image in your assignment where you see the (*I*). Otherwise there is no need to do so.

1. Variety in networks
Go to the site http://www.visualcomplexity.com. Select and list two projects describing a network. Answer the following about them (this may require going into the source webpage for the project, linked to from the visualcomplexity site).

• What do the nodes represent?
• What do the edges represent?
• Is the graph directed? Weighted?
• Can the data be represented as a bipartite graph? If so, what are the 'actors' and what are the 'events'?

2. A planar graph and layouts in Pajek
Download the file 'planarnet.net' from the ctools website.

• Open it in Pajek by either clicking on the yellow folder icon under the word "Network" or by selecting File>Network>Read from the main menu panel
  A report window should pop up confirming that the graph has been read and the filename and location will be displayed in the 'active' position of the network dropdown list.
• Visualize the network using Pajek's Draw>Draw command from the main menu panel.
  This will bring up the 'draw' window with its own menu bar at the top
• Reposition the vertices by clicking on them and holding down the mouse button while dragging them to a new location. Continue doing this until you have shown that the graph is planar (no edges cross have to cross ) (*I*)
  (If you think this is really fun to do in your spare time, go to http://www.planarity.net)
• Now let Pajek do the work for you by selecting from the draw toolbar several layout algorithms under 'Layout>Energy'. (*I*)
• Why did you select the layout algorithm you did?
• Did the layout leave any lines crossed? If you were to do this assignment over, what order would you do it in?

3. Bipartite graphs
Download the file actorsandmovies.net

• Open it in Pajek.
• This is a 2 mode network containing two classes of nodes, actors and movies. Create a 2-mode partition (Net>Partition>2-Mode). Now draw the network (Draw>Draw-Partition). The two classes of nodes should be colored differently. If labels are not shown, add them (Options>Mark Vertices Using>Labels). Apply your favorite layout algorithm. (*I*)
• Transfrom the network into a one-mode network (Net>Transform>2-Mode to 1-Mode>Rows). Draw the network (Draw>Draw). Qualitatively compare the structure of the 2-Mode to the 1-Mode network. Is there a loss of information?
• Show the weights on each edge using (Options>Lines>Mark Lines>with Values). What do the values represent?
• Compute the unweighted degree of each node (Net>Partitions>Degree>All). Next draw the network using (Draw>Draw-vector). How is the degree represented? Add the vector value to each vertex (it will be the degree/(max possible degree)) (Options>Mark Vertices Using>Vector Values). (*I*) Who are the most important actors using this measure?
• How does the boundary of the network (i.e. who is included) affect who is found to be most central? Load the file actorsandmoviesWithGere.net. It contains one extra actor, Richard Gere. Repeat the above procedure. In the 1-mode network of actors, is there a change in who is most central? What does this tell you about biases and boundaries in sample selection?
• Remove all edges between actors who have costarred in fewer than 3 movies (Net>Transform>Remove>Lines with value>Lower than). Which actors comprise the central core of this network?