[MAHOUT-369] Issues with DistributedLanczosSolver output

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.3, 0.4
• Fix Version/s: 0.5
• Component/s: classic
• Labels: DistributedLanczosSolver decomposer
• Assignee: Jake Mannix
• Reporter: Danny Leshem
• Created: 07/Apr/10 13:29
• Updated: 31/Jan/24 22:16
• Resolved: 05/Apr/11 00:24

Description

DistributedLanczosSolver (line 99) claims to persist eigenVectors.numRows() vectors.

    log.info("Persisting " + eigenVectors.numRows() + " eigenVectors and eigenValues to: " + outputPath);

However, a few lines later (line 106) we have

    for(int i=0; i<eigenVectors.numRows() - 1; i++) {
        ...
    }

which only persists eigenVectors.numRows()-1 vectors.

Seems like the most significant eigenvector (i.e. the one with the largest eigenvalue) is omitted... off by one bug?

Also, I think it would be better if the eigenvectors are persisted in reverse order, meaning the most significant vector is marked "0", the 2nd most significant is marked "1", etc.

This, for two reasons:
1) When performing another PCA on the same corpus (say, with more principal componenets), corresponding eigenvalues can be easily matched and compared.
2) Makes it easier to discard the least significant principal components, which for Lanczos decomposition are usually garbage.