Fix distributed circuit without gates execution

src/qibo/core/distcircuit.py

@@ -219,7 +219,7 @@ def execute(self, initial_state=None, nshots=None):
 
     def get_initial_state(self, state=None):
         """"""
-        if not self.queues.queues and self.queue:
+        if not self.queues.queues:
             self.queues.set(self.queue)
 
         if state is None:

src/qibo/core/distutils.py

@@ -116,15 +116,13 @@ def set(self, queue: List[gates.Gate]):
         This method also creates the ``DistributedQubits`` object holding the
         global qubits list.
         """
-        if not queue:
-            raise_error(RuntimeError, "No gates available to set for distributed run.")
-
         counter = self.count(queue, self.nqubits)
         if self.qubits is None:
             self.qubits = DistributedQubits(counter.argsort()[:self.nglobal],
                                             self.nqubits)
-        transformed_queue = self.transform(queue, counter)
-        self.create(transformed_queue)
+        if queue:
+            transformed_queue = self.transform(queue, counter)
+            self.create(transformed_queue)
 
     def _ids(self, calc_devices: Dict[str, int]) -> Tuple[str, List[int]]:
         """Generator of device piece indices."""

src/qibo/tests/test_core_distcircuit.py

@@ -72,11 +72,6 @@ def test_distributed_circuit_set_gates(backend):
     for queues in c.queues.queues[0]:
         assert len(queues) == 4
 
-    # Attempt to set gates before adding any gate
-    c = DistributedCircuit(6, devices)
-    with pytest.raises(RuntimeError):
-        c.queues.set(c.queue)
-
 
 def test_distributed_circuit_set_gates_controlled(backend):
     devices = {"/GPU:0": 2, "/GPU:1": 2}

src/qibo/tests/test_core_distcircuit_execution.py

@@ -1,7 +1,7 @@
 """Test functions defined in `qibo/core/distcircuit.py`."""
 import pytest
 import numpy as np
-from qibo import gates
+from qibo import K, gates
 from qibo.models import Circuit
 from qibo.core.distcircuit import DistributedCircuit
 from qibo.tests.utils import random_state
@@ -22,7 +22,7 @@ def test_distributed_circuit_execution(backend, accelerators, use_global_qubits)
     initial_state = random_state(c.nqubits)
     final_state = dist_c(np.copy(initial_state))
     target_state = c(np.copy(initial_state))
-    np.testing.assert_allclose(target_state, final_state)
+    K.assert_allclose(target_state, final_state)
 
 
 def test_distributed_circuit_execution_pretransformed(backend, accelerators):
@@ -39,7 +39,7 @@ def test_distributed_circuit_execution_pretransformed(backend, accelerators):
     initial_state = random_state(c.nqubits)
     final_state = dist_c(np.copy(initial_state))
     target_state = c(np.copy(initial_state))
-    np.testing.assert_allclose(target_state, final_state)
+    K.assert_allclose(target_state, final_state)
 
 
 def test_distributed_circuit_execution_with_swap(backend, accelerators):
@@ -55,7 +55,7 @@ def test_distributed_circuit_execution_with_swap(backend, accelerators):
     initial_state = random_state(c.nqubits)
     final_state = dist_c(np.copy(initial_state))
     target_state = c(np.copy(initial_state))
-    np.testing.assert_allclose(target_state, final_state)
+    K.assert_allclose(target_state, final_state)
 
 
 def test_distributed_circuit_execution_special_gate(backend, accelerators):
@@ -67,7 +67,7 @@ def test_distributed_circuit_execution_special_gate(backend, accelerators):
     c = Circuit(6)
     c.add(gates.Flatten(np.copy(initial_state)))
     c.add((gates.H(i) for i in range(dist_c.nlocal)))
-    np.testing.assert_allclose(dist_c(), c())
+    K.assert_allclose(dist_c(), c())
 
 
 def test_distributed_circuit_execution_controlled_gate(backend, accelerators):
@@ -81,7 +81,7 @@ def test_distributed_circuit_execution_controlled_gate(backend, accelerators):
     initial_state = random_state(c.nqubits)
     final_state = dist_c(np.copy(initial_state))
     target_state = c(np.copy(initial_state))
-    np.testing.assert_allclose(target_state, final_state)
+    K.assert_allclose(target_state, final_state)
 
 
 def test_distributed_circuit_execution_controlled_by_gates(backend, accelerators):
@@ -102,7 +102,7 @@ def test_distributed_circuit_execution_controlled_by_gates(backend, accelerators
     initial_state = random_state(c.nqubits)
     final_state = dist_c(np.copy(initial_state))
     target_state = c(np.copy(initial_state))
-    np.testing.assert_allclose(target_state, final_state)
+    K.assert_allclose(target_state, final_state)
 
 
 def test_distributed_circuit_execution_addition(backend, accelerators):
@@ -124,4 +124,22 @@ def test_distributed_circuit_execution_addition(backend, accelerators):
     c.add([gates.CNOT(i, i + 1) for i in range(5)])
     c.add([gates.Z(i) for i in range(6)])
     assert c.depth == dist_c.depth
-    np.testing.assert_allclose(dist_c(), c())
+    K.assert_allclose(dist_c(), c())
+
+
+def test_distributed_circuit_empty_execution(backend, accelerators):
+    # test executing a circuit with the default initial state
+    c = DistributedCircuit(5, accelerators)
+    final_state = c().state()
+    target_state = np.zeros_like(final_state)
+    target_state[0] = 1
+    K.assert_allclose(final_state, target_state)
+    # test re-executing the circuit with a given initial state
+    initial_state = random_state(c.nqubits)
+    K.assert_allclose(c(initial_state), initial_state)
+    # test executing a new circuit with a given initial state
+    c = DistributedCircuit(5, accelerators)
+    initial_state = random_state(c.nqubits)
+    K.assert_allclose(c(initial_state), initial_state)
+    # test re-executing the circuit with the default initial state
+    K.assert_allclose(c(), target_state)