Suppose this case, every user accesses every node of a system. Then the matrix would be all-1. However, the pairwise correlation now is not define because the all-1 matrix would be normalized as all-0. This could cause some problem.

However, this problem is by nature the problem of Correlation algorithm. A hack could be for dependand module to add a fake user or a fake rating. Example is in the uc_rec module.

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danithaca’s picture

danithaca commented
Status: Postponed » Closed (works as designed)

To fix this would make the code messy. A hack could be for dependand module to add a fake user or a fake rating. Example is in the uc_rec module.