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yap-6.3/packages/meld/examples/pagerank/pagerank.meld
Vítor Santos Costa 14bdc262df export TermToStream
2011-05-25 13:10:39 +01:00

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type rank(node, int, float).
type calcRank(node, int, sum float).
% type persistent numPages(node, int).
type persistent numPages(node, sum int).
type numLinks(node, sum int).
type path(node, node).
const damping = 0.85.
const num_iterations = 100.
% extern float to_float(int).
% extern float float_abs(float).
rank(A, 0, 1.0 / to_float(T)) :- numPages(A,T).
rank(A, I, V) :-
numLinks(B,L),
numPages(A, Ps),
calcRank(A, I, T),
% Before = I - 1,
% rank(A, Before, VOld),
V = damping + (1.0 - damping) * T,
I =< num_iterations.
% //float_abs((damping + (1.0 - damping) * T) - VOld) > 0.001.
calcRank(A, I + 1, 0.0) :-
rank(A, I, _).
calcRank(A, I + 1, O / to_float(C)) :-
edge(B, A),
rank(B, I, O),
numLinks(B, C).
numLinks(A, 1) :-
edge(A,B).
numPages(A, 1) :- path(A,_).
path(A, B) :-
edge(A,B).
path(A, B) :-
edge(B,A).
path(A, B) :-
edge(A,C),
path(C,B).
path(A, B) :-
edge(C,A),
path(C,B).