mahout源码分析之DistributedLanczosSolver（六）完结篇

Mahout版本：0.7，hadoop版本：1.0.4，jdk：1.7.0_25 64bit。

接上篇，分析完3个Job后得到继续往下：其实就剩下两个函数了：

 List<Map.Entry<MatrixSlice, EigenStatus>> prunedEigenMeta = pruneEigens(eigenMetaData);

    saveCleanEigens(new Configuration(), prunedEigenMeta);

看pruneEigens函数：

private List<Map.Entry<MatrixSlice, EigenStatus>> pruneEigens(Map<MatrixSlice, EigenStatus> eigenMetaData) {
    List<Map.Entry<MatrixSlice, EigenStatus>> prunedEigenMeta = Lists.newArrayList();

    for (Map.Entry<MatrixSlice, EigenStatus> entry : eigenMetaData.entrySet()) {
      if (Math.abs(1 - entry.getValue().getCosAngle()) < maxError && entry.getValue().getEigenValue() > minEigenValue) {
        prunedEigenMeta.add(entry);
      }
    }

看到这里其实是做筛选的，三个job生成了三个eigenStatus，每个eigenStatus都有一个cosAngle和eigenValue，用这两个参数来判断是否应该保留，这三个总结如下：

第一个；
resultantVector:
[-285.43017035605783, -61.30237570857193, -68.94124551381431, -520.2302762811703, -3232.201254912267, -32.31785150049481, -37.63572264009423, -12.025276244275622, -28.58260635344015, -6.8801603142200065, -28.491567864130573, -68.13521243410383, 4382.173720122737]
vector:
[0.01671441233225078, 0.0935655369363106, 0.09132650234523473, -0.0680324702834075, -0.9461123439509093, 0.10210271255992123, 0.10042714365337412, 0.11137954332150339, 0.10331974823993555, 0.10621406378767596, 0.10586960137353602, 0.09262650242313884, 0.09059904726143547]
eigenValue=newNorm/oldNorm=5479.061620543984/1=5479.061620543984;
cosAngle=resultantVector.dot(vector) / newNorm * oldNorm=0.6300724679092792

第二个：
resultantVector：
vector：
[0.01180448947054423, 0.001703710024210367, 0.002100735590662567, 0.014221147454610283, 0.09654151173375553, 0.0025666815984826535, 0.0026147055494762234, 1.753144283209579E-4, 0.0017595900141802873, 0.0049406361794682024, 7.881250692924197E-4, 0.002873479530226361, 0.9951286321096425]
eigenValue：6433335.386819993
cosAngle=0.9999998030863401
第三个：
vector:
[-0.2883450858059115, -0.29170231535763447, -0.29157035465385267, -0.28754185317979386, -0.26018076078737895, -0.2914154866344813, -0.2913995247546756, -0.2922103132689348, -0.2916837423401091, -0.29062644748002026, -0.2920066313645422, -0.2913135151887795, 0.03848561950058266]
eigenValue=1442.6143913921014
cosAngle=0.3671147029085018

可以看到只有第二个可以通过筛选，得到的prunedEigenMeta如下：

看下一个函数saveCleanEigens：

private void saveCleanEigens(Configuration conf, Collection<Map.Entry<MatrixSlice, EigenStatus>> prunedEigenMeta)
    throws IOException {
    Path path = new Path(outPath, CLEAN_EIGENVECTORS);
    FileSystem fs = FileSystem.get(path.toUri(), conf);
    SequenceFile.Writer seqWriter = new SequenceFile.Writer(fs, conf, path, IntWritable.class, VectorWritable.class);
    try {
      IntWritable iw = new IntWritable();
      int numEigensWritten = 0;
      for (Map.Entry<MatrixSlice, EigenStatus> pruneSlice : prunedEigenMeta) {
        MatrixSlice s = pruneSlice.getKey();
        EigenStatus meta = pruneSlice.getValue();
        EigenVector ev = new EigenVector(s.vector(),
                                         meta.getEigenValue(),
                                         Math.abs(1 - meta.getCosAngle()),
                                         s.index());
        //log.info("appending {} to {}", ev, path);
        Writable vw = new VectorWritable(ev);
        iw.set(s.index());
        seqWriter.append(iw, vw);

        // increment the number of eigenvectors written and see if we've
        // reached our specified limit, or if we wish to write all eigenvectors
        // (latter is built-in, since numEigensWritten will always be > 0
        numEigensWritten++;
        if (numEigensWritten == maxEigensToKeep) {
          log.info("{} of the {} total eigens have been written", maxEigensToKeep, prunedEigenMeta.size());
          break;
        }
      }
    } finally {
      Closeables.closeQuietly(seqWriter);
    }
    cleanedEigensPath = path;
  }

看保存的ev是什么吧：

还不是筛选出来的那个值，不过这里的误差就是1-cosAngle了；

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