Ben is Simple!

前两天Google的Pagerank更新了，Blog的Pr更新到了1，聊胜于无吧，为此还特意去搜索了一下Pr的定义，Sergey Brin和Larry Page当时还是斯坦福的学生。这里可以找到论文的全文。http://infolab.stanford.edu/~backrub/google.html

PageRank（PR）的定义如下：

Academic citation literature has been applied to the web, largely by counting citations or backlinks to a given page. This gives some approximation of a page’s importance or quality. PageRank extends this idea by not counting links from all pages equally, and by normalizing by the number of links on a page. PageRank is defined as follows:

We assume page A has pages T1…Tn which point to it (i.e., are citations). The parameter d is a damping factor which can be set between 0 and 1. We usually set d to 0.85. There are more details about d in the next section. Also C(A) is defined as the number of links going out of page A. The PageRank of a page A is given as follows:PR(A) = (1-d) + d (PR(T1)/C(T1) + … + PR(Tn)/C(Tn))

Note that the PageRanks form a probability distribution over web pages, so the sum of all web pages’ PageRanks will be one.

PageRank or PR(A) can be calculated using a simple iterative algorithm, and corresponds to the principal eigenvector of the normalized link matrix of the web. Also, a PageRank for 26 million web pages can be computed in a few hours on a medium size workstation. There are many other details which are beyond the scope of this paper.

大意就是上面的公式，链接你的页面，特别是高PR的页面越多，你的PR也越高。