Fix StatePreparation division by 0 and update docs

docs/projectq.ops.rst

@@ -49,6 +49,9 @@ The operations collection consists of various default gates and is a work-in-pro
 	projectq.ops.CZ
 	projectq.ops.Toffoli
 	projectq.ops.TimeEvolution
+	projectq.ops.UniformlyControlledRy
+	projectq.ops.UniformlyControlledRz
+	projectq.ops.StatePreparation
 
 
 Module contents

projectq/setups/decompositions/stateprep2cnot.py

@@ -66,7 +66,11 @@ def _decompose_state_preparation(cmd):
                 for block in range(2**(len(qureg)-target_qubit-1)):
                     a0 = abs_of_blocks[2*block]
                     a1 = abs_of_blocks[2*block+1]
-                    angles.append(-2. * math.acos(a0/math.sqrt(a0**2 + a1**2)))
+                    if a0 == 0 and a1 == 0:
+                        angles.append(0)
+                    else:
+                        angles.append(
+                            -2. * math.acos(a0 / math.sqrt(a0**2 + a1**2)))
                     abs_of_next_blocks.append(math.sqrt(a0**2 + a1**2))
                 UniformlyControlledRy(angles) | (qureg[(target_qubit+1):],
                                                  qureg[target_qubit])

projectq/setups/decompositions/stateprep2cnot_test.py

@@ -37,15 +37,19 @@ def test_wrong_final_state():
         stateprep2cnot._decompose_state_preparation(cmd)
 
 
+@pytest.mark.parametrize("zeros", [True, False])
 @pytest.mark.parametrize("n_qubits", [1, 2, 3, 4])
-def test_state_preparation(n_qubits):
+def test_state_preparation(n_qubits, zeros):
     engine_list = restrictedgateset.get_engine_list(
         one_qubit_gates=(Ry, Rz, Ph))
     eng = projectq.MainEngine(engine_list=engine_list)
     qureg = eng.allocate_qureg(n_qubits)
     eng.flush()
 
     f_state = [0.2+0.1*x*cmath.exp(0.1j+0.2j*x) for x in range(2**n_qubits)]
+    if zeros:
+        for i in range(2**(n_qubits-1)):
+            f_state[i] = 0
     norm = 0
     for amplitude in f_state:
         norm += abs(amplitude)**2