code: def _append_count_to_matrix(qtl_matrixfile, lod_threshold):
      
      if not os.path.exists(qtl_matrixfile):  # pragma: no cover
          raise MQ2Exception('File not found: "%s"' % qtl_matrixfile)
      matrix = read_input_file(qtl_matrixfile, sep=',')
      tmp = list(matrix[0])
      tmp.append('# QTLs')
      matrix[0] = tmp
      cnt = 1
      while cnt < len(matrix):
          row = list(matrix[cnt])
          nr_qtl = 0
          for cel in row[3:]:
              if cel and float(cel) > float(lod_threshold):
                  nr_qtl = nr_qtl + 1
          row.append(str(nr_qtl))
          matrix[cnt] = row
          cnt = cnt + 1
      write_matrix(qtl_matrixfile, matrix)
docs: Append an extra column at the end of the matrix file containing
      for each row (marker) the number of QTL found if the marker is known
      ie: Locus != ''
  
      :arg qtl_matrix, the matrix in which to save the output.
      :arg threshold, threshold used to determine if a given LOD value is
          reflective the presence of a QTL.