- 页码：第34页 2018-12-12 17:52:16
Milgram's six degrees and the Web's nineteen degrees suggest that small separations are common in just about every network scientists have had a chance to study.
Indeed, species in food webs appear to be on average two links away from each other; modules in the cell are separated on average by three chemical reactions; scientists in different fields of science are separated by four to six coauthorship links; and the neurons in the brain of the C. elegans worm are separated by fourteen synapses. Internet, a network of hundreds of thousands of routers, has a separation of ten.
P.35 Why? Consider a network in which the nodes have on average k links. This means that from a typical node we can reach k other nodes with one step. There are, however, k^2 nodes two links away and roughly k^d nodes d links away. Therefore, if k is large, for even small values of d the number of nodes you can reach can become very large. This explains why the average separation is so short in most networks.
The origin of small separation is a logarithmic term. The logarithm of even a very large number is rather small. The logarithm shrinks huge network and create small world around us.
p.37 The six/nineteen degrees phrase is deeply misleading because it suggest that things are easy to find in a small world. This could not be further from the truth! Even if it takes only one second to check a document, it would still take over 300 million years to get all documents that are nineteen clicks away!
The trick, of course, is that we do not follow all links. Rather, we used clues. By interpreting the links, we avoid having to check all the pages within nineteen degrees . While this method seems to be the most efficient, it almost always fails to find the shortest path.
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P.21: The premise of random network model is deeply egalitarian: We place the links com...
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