Fix a bug of the integer to binary converter (#1256)

* fix a bug of the integer to binary converter

* fix the return signature of QuadraticExpression.to_dict

Co-authored-by: Manoel Marques <Manoel.Marques@ibm.com>

qiskit/optimization/converters/integer_to_binary.py

@@ -185,18 +185,19 @@ def _substitute_int_var(self):
 
         # set linear constraints
         for constraint in self._src.linear_constraints:
-            linear, constant = self._convert_linear_coefficients_dict(constraint.linear.to_dict())
+            linear, constant = self._convert_linear_coefficients_dict(
+                constraint.linear.to_dict(use_name=True))
             self._dst.linear_constraint(
                 linear, constraint.sense, constraint.rhs - constant, constraint.name
             )
 
         # set quadratic constraints
         for constraint in self._src.quadratic_constraints:
             linear, linear_constant = self._convert_linear_coefficients_dict(
-                constraint.linear.to_dict()
+                constraint.linear.to_dict(use_name=True)
             )
             quadratic, q_linear, q_constant = self._convert_quadratic_coefficients_dict(
-                constraint.quadratic.to_dict()
+                constraint.quadratic.to_dict(use_name=True)
             )
 
             constant = linear_constant + q_constant

qiskit/optimization/problems/quadratic_expression.py

@@ -168,7 +168,7 @@ def to_dict(self, symmetric: bool = False, use_name: bool = False) \
                      self.quadratic_program.variables[j].name): v
                     for (i, j), v in coeffs.items()}
         else:
-            return dict(coeffs.items())
+            return {(int(i), int(j)): v for (i, j), v in coeffs.items()}
 
     def evaluate(self, x: Union[ndarray, List, Dict[Union[int, str], float]]) -> float:
         """Evaluate the quadratic expression for given variables: x * Q * x.

test/optimization/test_converters.py

@@ -679,6 +679,33 @@ def test_ising_to_quadraticprogram_quadratic_deprecated(self):
             quadratic.objective.quadratic.coefficients.toarray(), quadratic_matrix
         )
 
+    def test_integer_to_binary2(self):
+        """Test integer to binary variables 2"""
+        mod = QuadraticProgram()
+        mod.integer_var(name='x', lowerbound=0, upperbound=1)
+        mod.integer_var(name='y', lowerbound=0, upperbound=1)
+        mod.minimize(1, {'x': 1}, {('x', 'y'): 2})
+        mod.linear_constraint({'x': 1}, '==', 1)
+        mod.quadratic_constraint({'x': 1}, {('x', 'y'): 2}, '==', 1)
+        mod2 = IntegerToBinary().convert(mod)
+        self.assertListEqual([e.name+'@0' for e in mod.variables], [e.name for e in mod2.variables])
+        self.assertDictEqual(mod.objective.linear.to_dict(),
+                             mod2.objective.linear.to_dict())
+        self.assertDictEqual(mod.objective.quadratic.to_dict(),
+                             mod2.objective.quadratic.to_dict())
+        self.assertEqual(mod.get_num_linear_constraints(),
+                         mod2.get_num_linear_constraints())
+        for cst, cst2 in zip(mod.linear_constraints, mod2.linear_constraints):
+            self.assertDictEqual(cst.linear.to_dict(),
+                                 cst2.linear.to_dict())
+        self.assertEqual(mod.get_num_quadratic_constraints(),
+                         mod2.get_num_quadratic_constraints())
+        for cst, cst2 in zip(mod.quadratic_constraints, mod2.quadratic_constraints):
+            self.assertDictEqual(cst.linear.to_dict(),
+                                 cst2.linear.to_dict())
+            self.assertDictEqual(cst.quadratic.to_dict(),
+                                 cst2.quadratic.to_dict())
+
 
 if __name__ == '__main__':
     unittest.main()