/**
* Compute SALSA on graph initialized in initializeGraph() method.
*
* @param nIterations
*/
public void computeSALSA(int nIterations) {
for (int iter = 0; iter < nIterations; iter++) {
// Hubs: sum of authority-neighbors values divided by their degree
for (SalsaVertex hub : hubs.values()) {
double nbSum = 0.0;
// Update the degree because not all authorities were selected
int degree = 0;
for (int authId : hub.neighbors) {
SalsaVertex auth = authorities.get(authId);
if (auth != null) {
nbSum += auth.value / auth.degree;
degree++;
}
}
hub.value = nbSum;
hub.degree = degree;
}
// Authorities: push from authority side.
// First: set values to zero
for (SalsaVertex auth : authorities.values()) {
auth.value = 0;
}
// Then, push hubs values to their auths
for (SalsaVertex hub : hubs.values()) {
double myContribution = hub.value / hub.degree;
for (int authId : hub.neighbors) {
SalsaVertex auth = authorities.get(authId);
if (auth != null) {
auth.value += myContribution;
}
}
}
}
}
public void initializeGraph(Collection<Integer> circleOfTrust) {
hubs = new HashMap<Integer, SalsaVertex>(circleOfTrust.size(), 1.0f);
long t = System.currentTimeMillis();
int totalNeighbors = 0;
int cacheHits = 0;
HashSet<Integer> querySet = new HashSet<Integer>(circleOfTrust.size());
for (int v : circleOfTrust) {
hubs.put(v, new SalsaVertex(v));
if (cache.containsKey(v)) {
SalsaVertex hub = hubs.get(v);
hub.neighbors = cache.get(v);
hub.degree = hub.neighbors.size();
cacheHits++;
} else {
querySet.add(v);
}
}
/* Load neighbors of the circle of trust -- we probably would need some limitation here?? */
HashMap<Integer, ArrayList<Integer>> hubNeighbors = queryService.queryOutNeighbors(querySet);
long queryTime = System.currentTimeMillis() - t;
/* Initialize salsa */
t = System.currentTimeMillis();
for (Map.Entry<Integer, ArrayList<Integer>> entry : hubNeighbors.entrySet()) {
int hubId = entry.getKey();
SalsaVertex hub = hubs.get(hubId);
hub.neighbors = entry.getValue();
hub.degree = entry.getValue().size();
cache.put(hubId, entry.getValue());
}
// Count total neighbors
for (SalsaVertex hub : hubs.values()) {
totalNeighbors += hub.neighbors.size();
}
long salsaInitTime0 = System.currentTimeMillis() - t;
// We do not add neighbors to authorities -- we can push values to authorities
// and pull to hubs.
int[] authEntries = new int[totalNeighbors];
int j = 0;
for (SalsaVertex hub : hubs.values()) {
for (int authId : hub.neighbors) {
authEntries[j++] = authId;
}
}
assert (j == authEntries.length);
// Create map efficiently
Arrays.sort(authEntries);
int lastId = -1;
int count = 0;
// int filtered = 0;
ArrayList<SalsaVertex> tmpAuth = new ArrayList<SalsaVertex>(1 + authEntries.length / 100);
for (int i = 0; i < authEntries.length; i++) {
int authId = authEntries[i];
if (lastId != authId) {
if (lastId >= 0) {
if (count > FILTER_LIMIT) {
SalsaVertex auth = new SalsaVertex(lastId);
auth.degree = count;
tmpAuth.add(auth);
} else {
// filtered++;
}
count = 0;
}
lastId = authId;
}
count++;
}
authorities = new HashMap<Integer, SalsaVertex>(tmpAuth.size());
for (SalsaVertex auth : tmpAuth) {
authorities.put(auth.id, auth);
}
// NOTE: remove neighbors!
/*
long salsaInitTime = System.currentTimeMillis() - t;
logger.info("Query took: " + queryTime + " ms, circle of trust size=" + circleOfTrust.size() + ", cache size=" +
cache.size() + ", hits=" + cacheHits);
logger.info("Salsa init: " + salsaInitTime + " ms, first phase=" + salsaInitTime0 + " ms, hubs="
+ hubs.size() + ", auths=" + authorities.size());
logger.info("Filtered: " + filtered); */
}