Start deprecation of complex parameters in Qiskit Pulse (Qiskit#9735)

* Add warning and update tests

* Release notes

* Move warning to all Pulse objects.

* Fix releasenote typo

* Move warning to format_parameter_value

qiskit/pulse/parameter_manager.py

@@ -256,8 +256,8 @@ def _assign_parameter_expression(self, param_expr: ParameterExpression):
         updated = param_expr.parameters & self._param_map.keys()
         for param in updated:
             new_value = new_value.assign(param, self._param_map[param])
-
-        return format_parameter_value(new_value)
+        new_value = format_parameter_value(new_value)
+        return new_value
 
     def _update_parameter_manager(self, node: Union[Schedule, ScheduleBlock]):
         """A helper function to update parameter manager of pulse program."""

qiskit/pulse/utils.py

@@ -13,6 +13,7 @@
 """Module for common pulse programming utilities."""
 import functools
 from typing import List, Dict, Union
+import warnings
 
 import numpy as np
 
@@ -65,6 +66,19 @@ def format_parameter_value(
             evaluated = float(evaluated.real)
             if evaluated.is_integer():
                 evaluated = int(evaluated)
+        else:
+            warnings.warn(
+                "Assignment of complex values to ParameterExpression in Qiskit Pulse objects is "
+                "now pending deprecation. This will align the Pulse module with other modules "
+                "where such assignment wasn't possible to begin with. The typical use case for complex "
+                "parameters in the module was the SymbolicPulse library. As of Qiskit-Terra "
+                "0.23.0 all library pulses were converted from complex amplitude representation"
+                " to real representation using two floats (amp,angle), as used in the "
+                "ScalableSymbolicPulse class. This eliminated the need for complex parameters. "
+                "Any use of complex parameters (and particularly custom-built pulses) should be "
+                "converted in a similar fashion to avoid the use of complex parameters.",
+                PendingDeprecationWarning,
+            )
 
         return evaluated
     except TypeError:

releasenotes/notes/symbolic-pulse-complex-deprecation-89ecdf968b1a2d89.yaml

@@ -0,0 +1,12 @@
+---
+deprecations:
+  - |
+    Assignment of complex values to ``ParameterExpression`` in any Qiskit Pulse object
+    now raises a ``PendingDeprecationWarning``. This will align the Pulse module with
+    other modules where such assignment wasn't possible to begin with. The typical use
+    case for complex parameters in the module was the SymbolicPulse library. As of
+    Qiskit-Terra 0.23.0 all library pulses were converted from complex amplitude
+    representation to real representation using two floats (amp,angle), as used in the
+    ``ScalableSymbolicPulse`` class. This eliminated the need for complex parameters.
+    Any use of complex parameters (and particularly custom-built pulses) should be
+    converted in a similar fashion to avoid the use of complex parameters.

test/python/pulse/test_parameter_manager.py

@@ -201,7 +201,7 @@ class TestParameterSetter(ParameterTestBase):
     """Test setting parameters."""
 
     def test_set_parameter_to_channel(self):
-        """Test get parameters from channel."""
+        """Test set parameters from channel."""
         test_obj = pulse.DriveChannel(self.ch1 + self.ch2)
 
         value_dict = {self.ch1: 1, self.ch2: 2}
@@ -214,7 +214,7 @@ def test_set_parameter_to_channel(self):
         self.assertEqual(assigned, ref_obj)
 
     def test_set_parameter_to_pulse(self):
-        """Test get parameters from pulse instruction."""
+        """Test set parameters from pulse instruction."""
         test_obj = self.parametric_waveform1
 
         value_dict = {self.amp1_1: 0.1, self.amp1_2: 0.2, self.dur1: 160}
@@ -336,42 +336,47 @@ def test_nested_assignment_partial_bind(self):
         self.assertEqual(assigned, ref_obj)
 
     def test_complex_valued_parameter(self):
-        """Test complex valued parameter can be casted to a complex value."""
+        """Test complex valued parameter can be casted to a complex value,
+        but raises PendingDeprecationWarning.."""
         amp = Parameter("amp")
         test_obj = pulse.Constant(duration=160, amp=1j * amp)
 
         value_dict = {amp: 0.1}
 
         visitor = ParameterSetter(param_map=value_dict)
-        assigned = visitor.visit(test_obj)
+        with self.assertWarns(PendingDeprecationWarning):
+            assigned = visitor.visit(test_obj)
 
         ref_obj = pulse.Constant(duration=160, amp=1j * 0.1)
 
         self.assertEqual(assigned, ref_obj)
 
     def test_complex_value_to_parameter(self):
-        """Test complex value can be assigned to parameter object."""
+        """Test complex value can be assigned to parameter object,
+        but raises PendingDeprecationWarning."""
         amp = Parameter("amp")
         test_obj = pulse.Constant(duration=160, amp=amp)
 
         value_dict = {amp: 0.1j}
 
         visitor = ParameterSetter(param_map=value_dict)
-        assigned = visitor.visit(test_obj)
+        with self.assertWarns(PendingDeprecationWarning):
+            assigned = visitor.visit(test_obj)
 
         ref_obj = pulse.Constant(duration=160, amp=1j * 0.1)
 
         self.assertEqual(assigned, ref_obj)
 
     def test_complex_parameter_expression(self):
-        """Test assignment of complex-valued parameter expression to parameter."""
+        """Test assignment of complex-valued parameter expression to parameter,
+        but raises PendingDeprecationWarning."""
         amp = Parameter("amp")
 
         mag = Parameter("A")
         phi = Parameter("phi")
 
         test_obj = pulse.Constant(duration=160, amp=amp)
-
+        test_obj_copy = deepcopy(test_obj)
         # generate parameter expression
         value_dict = {amp: mag * np.exp(1j * phi)}
         visitor = ParameterSetter(param_map=value_dict)
@@ -380,13 +385,15 @@ def test_complex_parameter_expression(self):
         # generate complex value
         value_dict = {mag: 0.1, phi: 0.5}
         visitor = ParameterSetter(param_map=value_dict)
-        assigned = visitor.visit(assigned)
+        with self.assertWarns(PendingDeprecationWarning):
+            assigned = visitor.visit(assigned)
 
         # evaluated parameter expression: 0.0877582561890373 + 0.0479425538604203*I
         value_dict = {amp: 0.1 * np.exp(0.5j)}
-        visitor = ParameterSetter(param_map=value_dict)
-        ref_obj = visitor.visit(test_obj)
 
+        visitor = ParameterSetter(param_map=value_dict)
+        with self.assertWarns(PendingDeprecationWarning):
+            ref_obj = visitor.visit(test_obj_copy)
         self.assertEqual(assigned, ref_obj)
 
     def test_invalid_pulse_amplitude(self):