4.9.3 Example Custom PGX Algorithm: PageRank
The following is an implementation of pagerank
as a PGX algorithm:
import oracle.pgx.algorithm.PgxGraph;
import oracle.pgx.algorithm.Scalar;
import oracle.pgx.algorithm.VertexProperty;
import oracle.pgx.algorithm.annotations.GraphAlgorithm;
import oracle.pgx.algorithm.annotations.Out;
@GraphAlgorithm
public class Pagerank {
public void pagerank(PgxGraph G, double tol, double damp, int max_iter, boolean norm, @Out VertexProperty<Double> rank) {
Scalar<Double> diff = Scalar.create();
int cnt = 0;
double N = G.getNumVertices();
rank.setAll(1 / N);
do {
diff.set(0.0);
Scalar<Double> dangling_factor = Scalar.create(0d);
if (norm) {
dangling_factor.set(damp / N * G.getVertices().filter(v -> v.getOutDegree() == 0).sum(rank::get));
}
G.getVertices().forEach(t -> {
double in_sum = t.getInNeighbors().sum(w -> rank.get(w) / w.getOutDegree());
double val = (1 - damp) / N + damp * in_sum + dangling_factor.get();
diff.reduceAdd(Math.abs(val - rank.get(t)));
rank.setDeferred(t, val);
});
cnt++;
} while (diff.get() > tol && cnt < max_iter);
}
}
Parent topic: Using Custom PGX Graph Algorithms