code: public int trueNegatives(int classindex) {
      int tn = 0;
      for(int i = 0; i < confusion.length; i++) {
        for(int j = 0; j < confusion[i].length; j++) {
          if(i != classindex && j != classindex) {
            tn += confusion[i][j];
          }
        }
      }
      return tn;
    }
docs: The number of true negatives of the specified class.
  
  
  @param classindex the index of the class to retrieve the true negatives for
  @return the number of true negatives of the specified class