66 lines
1.2 KiB
Mathematica
66 lines
1.2 KiB
Mathematica
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function x = pagerank(U,G,p)
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% PAGERANK Google's PageRank
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% pagerank(U,G,p) uses the URLs and adjacency matrix produced by SURFER,
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% together with a damping factory p, (default is .85), to compute and plot
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% a bar graph of page rank, and print the dominant URLs in page rank order.
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% x = pagerank(U,G,p) returns the page ranks instead of printing.
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% See also SURFER, SPY.
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if nargin < 3, p = .85; end
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if(ischar(U))
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U=cellstr(U);
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end
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if(isreal(U))
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U=(num2cell(U));
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end
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% Eliminate any self-referential links
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G = G - diag(diag(G));
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% c = out-degree, r = in-degree
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n = size(G,1);
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c = sum(G,1);
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r = sum(G,2);
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% Scale column sums to be 1 (or 0 where there are no out links).
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k = find(c~=0);
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D = sparse(k,k,1./c(k),n,n);
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% Solve (I - p*G*D)*x = e
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e = ones(n,1);
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I = speye(n,n);
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x = (I - p*G*D)\e;
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% Normalize so that sum(x) == 1.
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x = x/sum(x);
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% Bar graph of page rank.
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shg
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bar(x)
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title('Page Rank')
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% Print URLs in page rank order.
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if nargout < 1
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[~,q] = sort(-x);
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disp(' page-rank in out url')
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k = 1;
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while (k <= n) && (x(q(k)) >= .005)
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j = q(k);
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temp1 = r(j);
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temp2 = c(j);
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fprintf(' %3.0f %8.4f %4.0f %4.0f %s\n', j,x(j),full(temp1),full(temp2),U{j})
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k = k+1;
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end
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end
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