Description:
            Position k breaking
        Parameters:
            k: position k is used for the breaking

def _pos(self, k):
        """
        Description:
            Position k breaking
        Parameters:
            k: position k is used for the breaking
        """
        if k < 2:
            raise ValueError("k smaller than 2")
        G = np.zeros((self.m, self.m))
        for i in range(self.m):
            for j in range(self.m):
                if i == j:
                    continue
                if i < k or j < k:
                    continue
                if i == k or j == k:
                    G[i][j] = 1
        return G