code: def _top(self, k):
          
          if k > self.m:
              raise ValueError("k larger than the number of alternatives")
          G = np.ones((self.m, self.m))
          #np.fill_diagonal(G, 0)  # erroneous code from prefpy
          for i in range(self.m):
              for j in range(self.m):
                  if i == j:
                      continue
                  if i > k and j > k:
                      G[i][j] = 0
          return G
docs: Description:
              Top k breaking
          Parameters:
              k: the number of alternatives to break from highest rank