code: # -*- coding: utf-8 -*-
  
  # This code is part of Qiskit.
  #
  # (C) Copyright IBM 2018, 2020.
  #
  # This code is licensed under the Apache License, Version 2.0. You may
  # obtain a copy of this license in the LICENSE.txt file in the root directory
  # of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
  #
  # Any modifications or derivative works of this code must retain this
  # copyright notice, and modified files need to carry a notice indicating
  # that they have been altered from the originals.
  
  """ Test Vertex Cover """
  
  import unittest
  from test.optimization import QiskitOptimizationTestCase
  import numpy as np
  from qiskit import BasicAer
  
  from qiskit.aqua import aqua_globals, QuantumInstance
  from qiskit.optimization.applications.ising import vertex_cover
  from qiskit.optimization.applications.ising.common import random_graph, sample_most_likely
  from qiskit.aqua.algorithms import NumPyMinimumEigensolver, VQE
  from qiskit.aqua.components.variational_forms import RYRZ
  from qiskit.aqua.components.optimizers import SPSA
  
  
  class TestVertexCover(QiskitOptimizationTestCase):
      """Cplex Ising tests."""
  
      def setUp(self):
          super().setUp()
          self.seed = 100
          aqua_globals.random_seed = self.seed
          self.num_nodes = 3
          self.w = random_graph(self.num_nodes, edge_prob=0.8, weight_range=10)
          self.qubit_op, self.offset = vertex_cover.get_operator(self.w)
  
      def _brute_force(self):
          # brute-force way
          def bitfield(n, length):
              result = np.binary_repr(n, length)
              return [int(digit) for digit in result]  # [2:] to chop off the "0b" part
  
          nodes = self.num_nodes
          maximum = 2 ** nodes
          minimal_v = np.inf
          for i in range(maximum):
              cur = bitfield(i, nodes)
  
              cur_v = vertex_cover.check_full_edge_coverage(np.array(cur), self.w)
              if cur_v:
                  nonzerocount = np.count_nonzero(cur)
                  if nonzerocount < minimal_v:
                      minimal_v = nonzerocount
  
          return minimal_v
  
      def test_vertex_cover(self):
          """ Vertex Cover test """
          algo = NumPyMinimumEigensolver(self.qubit_op, aux_operators=[])
          result = algo.run()
          x = sample_most_likely(result.eigenstate)
          sol = vertex_cover.get_graph_solution(x)
          np.testing.assert_array_equal(sol, [0, 1, 1])
          oracle = self._brute_force()
          self.assertEqual(np.count_nonzero(sol), oracle)
  
      def test_vertex_cover_vqe(self):
          """ Vertex Cover VQE test """
          aqua_globals.random_seed = self.seed
  
          result = VQE(self.qubit_op,
                       RYRZ(self.qubit_op.num_qubits, depth=3),
                       SPSA(max_trials=200),
                       max_evals_grouped=2).run(
                           QuantumInstance(BasicAer.get_backend('qasm_simulator'),
                                           seed_simulator=aqua_globals.random_seed,
                                           seed_transpiler=aqua_globals.random_seed))
  
          x = sample_most_likely(result['eigvecs'][0])
          sol = vertex_cover.get_graph_solution(x)
          oracle = self._brute_force()
          self.assertEqual(np.count_nonzero(sol), oracle)
  
  
  if __name__ == '__main__':
      unittest.main()
  
apis: numpy.array numpy.count_nonzero numpy.testing.assert_array_equal numpy.binary_repr