Determine the max number of ancillae for all ESOPs (TruthTableOracle …

…fix) (qiskit-community#1128) * determine the max number of ancillae for all ESOPs * fix for when no ancillae are needed Co-authored-by: Steve Wood <40241007+woodsp-ibm@users.noreply.github.com>
pbark · Sep 16, 2020 · f544bbc · f544bbc
1 parent 6cf8e4d
commit f544bbc
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Showing 2 changed files with 29 additions and 17 deletions.
diff --git a/qiskit/aqua/circuits/boolean_logical_circuits.py b/qiskit/aqua/circuits/boolean_logical_circuits.py
@@ -182,6 +182,27 @@ def _set_up_register(num_qubits_needed, provided_register, description):
 
         return None
 
+    def compute_num_ancillae(self, mct_mode='basic'):
+        """ returns the number of ancillary qubits needed """
+        max_num_ancillae = max(
+            max(
+                self._num_clauses if self._clause_register else 0,
+                self._max_clause_size
+            ) - 2,
+            0
+        )
+        num_ancillae = 0
+        if mct_mode in ('basic', 'basic-dirty-ancilla'):
+            num_ancillae = max_num_ancillae
+        elif mct_mode == 'advanced':
+            if max_num_ancillae >= 3:
+                num_ancillae = 1
+        elif mct_mode == 'noancilla':
+            pass
+        else:
+            raise ValueError('Unsupported MCT mode {}.'.format(mct_mode))
+        return num_ancillae
+
     def _set_up_circuit(
             self,
             circuit=None,
@@ -204,23 +225,7 @@ def _set_up_circuit(
         )
         self._output_idx = output_idx if output_idx else 0
 
-        max_num_ancillae = max(
-            max(
-                self._num_clauses if self._clause_register else 0,
-                self._max_clause_size
-            ) - 2,
-            0
-        )
-        num_ancillae = 0
-        if mct_mode in ('basic', 'basic-dirty-ancilla'):
-            num_ancillae = max_num_ancillae
-        elif mct_mode == 'advanced':
-            if max_num_ancillae >= 3:
-                num_ancillae = 1
-        elif mct_mode == 'noancilla':
-            pass
-        else:
-            raise ValueError('Unsupported MCT mode {}.'.format(mct_mode))
+        num_ancillae = self.compute_num_ancillae(mct_mode)
 
         self._ancillary_register = BooleanLogicNormalForm._set_up_register(
             num_ancillae, ancillary_register, 'ancilla'

diff --git a/qiskit/aqua/components/oracles/truth_table_oracle.py b/qiskit/aqua/components/oracles/truth_table_oracle.py
@@ -206,11 +206,18 @@ def construct_circuit(self):
         self._circuit = QuantumCircuit()
         self._output_register = QuantumRegister(self._num_outputs, name='o')
         if self._esops:
+            num_ancillae, self._ancillary_register = 0, None
+            for i, e in enumerate(self._esops):
+                num_ancillae = max(num_ancillae, e.compute_num_ancillae(self._mct_mode))
+            if num_ancillae > 0:
+                self._ancillary_register = QuantumRegister(num_ancillae, name='a')
+
             for i, e in enumerate(self._esops):
                 if e is not None:
                     ci = e.construct_circuit(
                         output_register=self._output_register,
                         output_idx=i,
+                        ancillary_register=self._ancillary_register,
                         mct_mode=self._mct_mode
                     )
                     self._circuit += ci