public GraphTableRows QueryN1(int n1)
            {
                GraphTableRows rows = new GraphTableRows();

                foreach (GraphTableRow row in _rows)
                {
                    if (row.N1 == n1)
                    {
                        rows.Add(row);
                    }
                }
                return(rows);
            }
 public void Add(int n1, int n2, int eid, double length)
 {
     _rows.Add(new GraphTableRow(
                   n1, n2, eid, length, length));
 }