code: public Iterator<MatrixEntry> iterator() {
          try {
              return MatrixIO.getMatrixFileIterator(matrixFile, format);
          } catch (IOException ioe) {
              throw new IOError(ioe);
          }
      }
docs: Returns an iterator over all the entries in the matrix.  The order in
  which entries are returned is format-specific; no guarantee is provided
  about the ordering.