Sebastian Schelter created MAHOUT-1144:
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Summary: Wrong normalization in SVD++
Key: MAHOUT-1144
URL: https://issues.apache.org/jira/browse/MAHOUT-1144
Project: Mahout
Issue Type: Bug
Components: Collaborative Filtering
Affects Versions: 0.8
Reporter: Sebastian Schelter
Assignee: Sean Owen
Reported by Agnonchik:
Seems that I have found a discrepancy of this implementation from the original
Yehuda Koren's SVD++ algorithm.
line 140:
double denominator = Math.sqrt(itemsByUser.size());
should be
double denominator = Math.sqrt(itemsByUser.get(u).size());
line 164:
double denominator = Math.sqrt(itemsByUser.size());
should be
double denominator = Math.sqrt(itemsByUser.get(u).size());
The sum of y parameters should be normalized by square root of number of items
for which user u provided implicit feedback. Am I right?
Currently, it is normalized by square root of number of users not items.
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