/** Computes the next step of the Power Method. */
public void step() throws IOException {
double[] oldRank = rank, newRank = previousRank;
DoubleArrays.fill(newRank, 0.0);
// for each node, calculate its outdegree and redistribute its rank among pointed nodes
double accum = 0.0;
progressLogger.expectedUpdates = numNodes;
progressLogger.start("Iteration " + (++iterationNumber) + "...");
final ArcLabelledNodeIterator nodeIterator = g.nodeIterator();
int i, outdegree, j, n = numNodes;
int[] succ;
Label[] lab;
while (n-- != 0) {
i = nodeIterator.nextInt();
outdegree = nodeIterator.outdegree();
if (outdegree == 0 || buckets != null && buckets.get(i)) accum += oldRank[i];
else {
j = outdegree;
succ = nodeIterator.successorArray();
lab = nodeIterator.labelArray();
while (j-- != 0) {
newRank[succ[j]] += (oldRank[i] * lab[j].getFloat()) / sumoutweight[i];
}
}
progressLogger.update();
}
progressLogger.done();
final double accumOverNumNodes = accum / numNodes;
final double oneOverNumNodes = 1.0 / numNodes;
if (preference != null)
if (preferentialAdjustment == null)
for (i = numNodes; i-- != 0; )
newRank[i] =
alpha * newRank[i]
+ (1 - alpha) * preference.getDouble(i)
+ alpha * accumOverNumNodes;
else
for (i = numNodes; i-- != 0; )
newRank[i] =
alpha * newRank[i]
+ (1 - alpha) * preference.getDouble(i)
+ alpha * accum * preferentialAdjustment.getDouble(i);
else if (preferentialAdjustment == null)
for (i = numNodes; i-- != 0; )
newRank[i] = alpha * newRank[i] + (1 - alpha) * oneOverNumNodes + alpha * accumOverNumNodes;
else
for (i = numNodes; i-- != 0; )
newRank[i] =
alpha * newRank[i]
+ (1 - alpha) * oneOverNumNodes
+ alpha * accum * preferentialAdjustment.getDouble(i);
// make the rank just computed the new rank
rank = newRank;
previousRank = oldRank;
// Compute derivatives.
n = iterationNumber;
if (subset == null) {
for (i = 0; i < order.length; i++) {
final int k = order[i];
final double alphak = Math.pow(alpha, k);
final double nFallingK = Util.falling(n, k);
for (j = 0; j < numNodes; j++)
derivative[i][j] += nFallingK * (rank[j] - previousRank[j]) / alphak;
}
} else {
for (i = 0; i < order.length; i++) {
final int k = order[i];
final double alphak = Math.pow(alpha, k);
final double nFallingK = Util.falling(n, k);
for (int t : subset) derivative[i][t] += nFallingK * (rank[t] - previousRank[t]) / alphak;
}
}
// Compute coefficients, if required.
if (coeffBasename != null) {
final DataOutputStream coefficients =
new DataOutputStream(
new FastBufferedOutputStream(
new FileOutputStream(coeffBasename + "-" + (iterationNumber))));
final double alphaN = Math.pow(alpha, n);
for (i = 0; i < numNodes; i++) coefficients.writeDouble((rank[i] - previousRank[i]) / alphaN);
coefficients.close();
}
}
