Mahout
  1. Mahout
  2. MAHOUT-369

Issues with DistributedLanczosSolver output

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      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.

      1. ASF.LICENSE.NOT.GRANTED--MAHOUT-369.patch
        2 kB
        Danny Leshem
      2. MAHOUT-369.diff
        23 kB
        Jake Mannix

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          • Assignee:
            Jake Mannix
            Reporter:
            Danny Leshem
          • Votes:
            3 Vote for this issue
            Watchers:
            5 Start watching this issue

            Dates

            • Created:
              Updated:
              Resolved:

              Development