Issues with DistributedLanczosSolver output
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Key: MAHOUT-369
URL: https://issues.apache.org/jira/browse/MAHOUT-369
Project: Mahout
Issue Type: Bug
Components: Math
Affects Versions: 0.3, 0.4
Reporter: Danny Leshem
DistributedLanczosSolver (line 99) claims to persist eigenVectors.numRows()
vectors.
{code}
log.info("Persisting " + eigenVectors.numRows() + " eigenVectors and
eigenValues to: " + outputPath);
{code}
However, a few lines later (line 106) we have
{code}
for(int i=0; i<eigenVectors.numRows() - 1; i++) {
...
}
{code}
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 garabage.
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