There may be something wrong about ItemKNN.java

[hegongshan]

Hi, Prof. He!
In the ItemKNN.java, the similarity matrix is a diagonal matrix but the method buildModel_items only seems to calculate the values in the lower triangular part and doesn't assign the values to the symmetry elements.
The experimental results show that there are some differences between using itemCount && j != i and itemCount in line 5 (line 71 of the original code).

protected void buildModel_items(int startItem, int endItem) {
		// Build the similarity matrix for selected items.
		for (int i = startItem; i < endItem; i++) {
			HashMap<Integer, Double> map_item_score = new HashMap<Integer, Double>();
			for (int j = 0; j < itemCount && j != i; j++) {
				// Cosine similarity
				double score = trainMatrix.getColRef(i).innerProduct(trainMatrix.getColRef(j));
				if (score != 0) {
					score /= (lengths[i] * lengths[j]);
					map_item_score.put(j, score);
				}
			}
			if (K <= 0) { // All neighbors
				for (int j : map_item_score.keySet()) {
					similarity.setValue(i, j, map_item_score.get(j));
				}
			} else { // Only K nearest neighbors
				for (int j : CommonUtils.TopKeysByValue(map_item_score, K, null)) {
					similarity.setValue(i, j, map_item_score.get(j));
				}
			} // end if
		} // end for

sigir16-eals/src/algorithms/ItemKNN.java

Line 71 in 993d19f

for (int j = 0; j < itemCount & j != i; j ++) {