Fix grover optimizer (qiskit-community/qiskit-aqua#966)

* fix grover optimizer

grover optimizer didn't handle maximization correctly.

* Update test_grover_optimizer.py

* use aqua_globals as RNG

* fix seed for tests

Co-authored-by: Cryoris <jules.gacon@googlemail.com>

qiskit/optimization/algorithms/grover_optimizer.py

@@ -17,11 +17,10 @@
 import logging
 from typing import Optional, Dict, Union, Tuple
 import math
-import random
 import numpy as np
 from qiskit import QuantumCircuit
 from qiskit.providers import BaseBackend
-from qiskit.aqua import QuantumInstance
+from qiskit.aqua import QuantumInstance, aqua_globals
 from qiskit.aqua.algorithms.amplitude_amplifiers.grover import Grover
 from ..exceptions import QiskitOptimizationError
 from .optimization_algorithm import OptimizationAlgorithm, OptimizationResult
@@ -116,6 +115,16 @@ def solve(self, problem: QuadraticProgram) -> OptimizationResult:
         qubo_converter = QuadraticProgramToQubo()
         problem_ = qubo_converter.encode(problem)
 
+        # convert to minimization problem
+        sense = problem_.objective.sense
+        if sense == problem_.objective.Sense.MAXIMIZE:
+            problem_.objective.sense = problem_.objective.Sense.MINIMIZE
+            problem_.objective.constant = -problem_.objective.constant
+            for i, v in problem_.objective.linear.to_dict().items():
+                problem_.objective.linear[i] = -v
+            for (i, j), v in problem_.objective.quadratic.to_dict().items():
+                problem_.objective.quadratic[i, j] = -v
+
         # Variables for tracking the optimum.
         optimum_found = False
         optimum_key = math.inf
@@ -156,7 +165,7 @@ def solve(self, problem: QuadraticProgram) -> OptimizationResult:
             while not improvement_found:
                 # Determine the number of rotations.
                 loops_with_no_improvement += 1
-                rotation_count = int(np.ceil(random.uniform(0, m-1)))
+                rotation_count = int(np.ceil(aqua_globals.random.uniform(0, m-1)))
                 rotations += rotation_count
 
                 # Apply Grover's Algorithm to find values below the threshold.
@@ -218,7 +227,10 @@ def solve(self, problem: QuadraticProgram) -> OptimizationResult:
 
         # Build the results object.
         grover_results = GroverOptimizationResults(operation_count, n_key, n_value, func_dict)
-        result = OptimizationResult(x=opt_x, fval=solutions[optimum_key],
+        fval = solutions[optimum_key]
+        if sense == problem_.objective.Sense.MAXIMIZE:
+            fval = -fval
+        result = OptimizationResult(x=opt_x, fval=fval,
                                     results={"grover_results": grover_results,
                                              "qubo_converter": qubo_converter})
 
@@ -234,7 +246,7 @@ def _measure(self, circuit: QuantumCircuit, n_key: int, n_value: int) -> str:
 
         # Pick a random outcome.
         freq[len(freq)-1] = (freq[len(freq)-1][0], 1 - sum([x[1] for x in freq[0:len(freq)-1]]))
-        idx = np.random.choice(len(freq), 1, p=[x[1] for x in freq])[0]
+        idx = aqua_globals.random.choice(len(freq), 1, p=[x[1] for x in freq])[0]
         logger.info('Frequencies: %s', freq)
 
         return freq[idx][0]

qiskit/optimization/converters/quadratic_program_to_negative_value_oracle.py

@@ -42,14 +42,14 @@ class QuadraticProgramToNegativeValueOracle:
             arxiv:1912.04088.
     """
 
-    def __init__(self, num_output_qubits: int, measurement: bool = False) -> None:
+    def __init__(self, num_value_qubits: int, measurement: bool = False) -> None:
         """
         Args:
-            num_output_qubits: The number of qubits required to represent the output.
+            num_value_qubits: The number of qubits required to represent the output.
             measurement: Whether the A operator contains measurements.
         """
         self._num_key = 0
-        self._num_value = num_output_qubits
+        self._num_value = num_value_qubits
         self._measurement = measurement
 
     def encode(self, problem: QuadraticProgram) -> \

test/optimization/test_grover_optimizer.py

@@ -16,8 +16,6 @@
 
 import unittest
 from test.optimization import QiskitOptimizationTestCase
-import random
-import numpy
 from docplex.mp.model import Model
 from qiskit import Aer
 from qiskit.aqua import aqua_globals, QuantumInstance
@@ -31,9 +29,7 @@ class TestGroverOptimizer(QiskitOptimizationTestCase):
 
     def setUp(self):
         super().setUp()
-        random.seed = 2
-        numpy.random.seed = 42
-        aqua_globals.seed = 42
+        aqua_globals.random_seed = 1
         self.q_instance = QuantumInstance(Aer.get_backend('statevector_simulator'),
                                           seed_simulator=921, seed_transpiler=200)
 
@@ -81,6 +77,23 @@ def test_qubo_gas_int_simple(self):
         results = gmf.solve(op)
         self.validate_results(op, results)
 
+    def test_qubo_gas_int_simple_maximize(self):
+        """Test for simple case, but with maximization."""
+
+        # Input.
+        model = Model()
+        x_0 = model.binary_var(name='x0')
+        x_1 = model.binary_var(name='x1')
+        model.maximize(-x_0+2*x_1)
+        op = QuadraticProgram()
+        op.from_docplex(model)
+
+        # Get the optimum key and value.
+        n_iter = 8
+        gmf = GroverOptimizer(4, num_iterations=n_iter, quantum_instance=self.q_instance)
+        results = gmf.solve(op)
+        self.validate_results(op, results)
+
     def test_qubo_gas_int_paper_example(self):
         """Test the example from https://arxiv.org/abs/1912.04088."""