[Hama Wiki] Update of "MatMult" by udanax

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The following page has been changed by udanax:
http://wiki.apache.org/hama/MatMult

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=== Multiplication of Hama matrices ===

{{{
  public static void main() throws IOException {
    HamaConfiguration conf = new HamaConfiguration();
    Matrix m1 = DenseMatrix.random(conf, 1000, 1000);
    Matrix m2 = DenseMatrix.random(conf, 1000, 1000);

    Matrix result = m1.mult(m2);
  }
}}}

=== Multiplication example of file matrices on HDFS ===
{{{
public class FileMatrixBlockMult extends AbstractExample {
  final static Log LOG = LogFactory.getLog(FileMatrixBlockMult.class.getName());
  private static int BLOCKSIZE;
  private static int ROWS;
  private static int COLUMNS;

  /**
   * Collect blocks from sequence file,
   */
  public static class MyMapper extends CollectBlocksMapReduceBase implements
      CollectBlocksMap<IntWritable, MapWritable> {
    private MapWritable value;

    @Override
    public void map(IntWritable key, MapWritable value,
        OutputCollector<BlockID, VectorWritable> output, Reporter reporter)
        throws IOException {
      int startColumn;
      int endColumn;
      int blkRow = key.get() / mBlockRowSize;
      this.value = value;

      int i = 0;
      do {
        startColumn = i * mBlockColSize;
        endColumn = startColumn + mBlockColSize - 1;
        if (endColumn >= mColumns) // the last sub vector
          endColumn = mColumns - 1;
        output.collect(new BlockID(blkRow, i), new VectorWritable(key.get(),
            subVector(startColumn, endColumn)));

        i++;
      } while (endColumn < (mColumns - 1));
    }

    private DenseVector subVector(int i0, int i1) {
      DenseVector res = new DenseVector();
      for (int i = i0; i <= i1; i++) {
        res.set(i, ((DoubleWritable) this.value.get(new IntWritable(i))).get());
      }

      return res;
    }
  }

  /**
   * @param a the path of matrix A
   * @param b the path of matrix B
   * @return the result C
   * @throws IOException
   */
  private static DenseMatrix matMult(Path a, Path b) throws IOException {
    HamaConfiguration conf = new HamaConfiguration();
    Matrix collectionTable = new DenseMatrix(conf);

    collectBlocksFromFile(a, true, collectionTable.getPath(), conf);
    collectBlocksFromFile(b, false, collectionTable.getPath(), conf);

    DenseMatrix result = new DenseMatrix(conf);
    JobConf jobConf = new JobConf(conf);
    jobConf.setJobName("multiplication MR job : " + result.getPath());

    BlockMultiplyMap.initJob(collectionTable.getPath(), BlockMultiplyMap.class,
        BlockID.class, BlockWritable.class, jobConf);
    BlockMultiplyReduce.initJob(result.getPath(), BlockMultiplyReduce.class,
        jobConf);

    JobManager.execute(jobConf, result);

    return result;
  }

  public static void main(String[] args) throws IOException {
    if (args.length < 5) {
      System.out
          .println("multfiles  [-m maps] [-r reduces] <seqfile1> <seqfile1> <blocks> <rows> <columns>");
      System.exit(-1);
    } else {
      parseArgs(args);
    }

    Path a = new Path(ARGS.get(0));
    Path b = new Path(ARGS.get(1));

    BLOCKSIZE = Integer.parseInt(ARGS.get(2));
    // You should know dimensions
    ROWS = Integer.parseInt(ARGS.get(3));
    COLUMNS = Integer.parseInt(ARGS.get(4));

    DenseMatrix result = matMult(a, b);
    System.out.println("result: " + result.getRows() + " by "
        + result.getColumns());
  }

  private static void collectBlocksFromFile(Path path, boolean b,
      String collectionTable, HamaConfiguration conf) throws IOException {
    JobConf jobConf = new JobConf(conf);
    jobConf.setJobName("Blocking MR job" + path);

    jobConf.setMapperClass(MyMapper.class);
    jobConf.setInputFormat(SequenceFileInputFormat.class);
    FileInputFormat.addInputPath(jobConf, path);

    MyMapper.initJob(collectionTable, b, BLOCKSIZE, ROWS, COLUMNS, jobConf);
    JobClient.runJob(jobConf);
  }
}
}}}