protected void addToCentroid(Matrix m, PositionWeightMatrix pwm) {
   for (int i = 0; i < m.getColumnDimension(); i++) {
     PositionWeightColumn c = pwm.get(i);
     for (int j = 0; j < m.getRowDimension(); j++) {
       m.set(j, i, m.get(j, i) + c.getWeight(j));
     }
   }
 }
 public void write(BufferedWriter bw, NumberFormat formatter) throws IOException {
   bw.write(">" + name);
   bw.newLine();
   if (size() > 0) {
     int rows = get(0).getAlphabetSize();
     for (int i = 0; i < rows; i++) {
       Iterator<PositionWeightColumn> colIt = iterator();
       while (colIt.hasNext()) {
         PositionWeightColumn col = colIt.next();
         bw.write(formatter.format(col.getWeight(i)));
         if (colIt.hasNext()) {
           bw.write("\t");
         }
       }
       bw.newLine();
     }
   }
 }