[BioPython] kcluster and distances

[Scott Rifkin]

The euclidean distance function in cluster.c is:

{ double result = 0.;
  double tweight = 0;
  int i;
  if (transpose==0) /* Calculate the distance between two rows */
  { for (i = 0; i < n; i++)
    { if (mask1[index1][i] && mask2[index2][i])
      { double term = data1[index1][i] - data2[index2][i];
        result = result + weight[i]*term*term;
        tweight += weight[i];
      }
    }
  }
  else
  { for (i = 0; i < n; i++)
    { if (mask1[i][index1] && mask2[i][index2])
      { double term = data1[i][index1] - data2[i][index2];
        result = result + weight[i]*term*term;
        tweight += weight[i];
      }
    }
  }
  if (!tweight) return 0; /* usually due to empty clusters */
  result /= tweight;
  result *= n;
  return result;
}

why at the end is the result multiplied by n?  and why isn't the square 
root of result given as the distance?

thanks
scott rifkin