public double distance(SparseVector a, SparseVector b) {
// double ret = a.dotProduct (b) /
// Math.sqrt (a.dotProduct (a) * b.dotProduct (b));
// gmann : twoNorm() more efficient than a.dotProduct(a)
double ret = a.dotProduct(b) / (a.twoNorm() * b.twoNorm());
return 1.0 - ret;
}
public double distance(SparseVector a, int hashCodeA, SparseVector b, int hashCodeB) {
Double cachedA = (Double) hash.get(new Integer(hashCodeA));
Double cachedB = (Double) hash.get(new Integer(hashCodeB));
if (a == null || b == null) return 1.0;
if (cachedA == null) {
cachedA = new Double(a.dotProduct(a));
hash.put(new Integer(hashCodeA), cachedA);
}
if (cachedB == null) {
cachedB = new Double(b.dotProduct(b));
hash.put(new Integer(hashCodeB), cachedB);
}
double ab = a.dotProduct(b);
if (cachedA == null || cachedB == null) {
throw new IllegalStateException("cachedValues null");
}
double ret = a.dotProduct(b) / Math.sqrt(cachedA.doubleValue() * cachedB.doubleValue());
return 1.0 - ret;
}