revert computing matrix for trivial matrices (#4354)

Qiskit · May 28, 2020 · dcbabda · dcbabda
1 parent f29bf76
commit dcbabda
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Showing 3 changed files with 50 additions and 12 deletions.
diff --git a/qiskit/circuit/library/standard_gates/h.py b/qiskit/circuit/library/standard_gates/h.py
@@ -18,7 +18,6 @@
 from qiskit.circuit.controlledgate import ControlledGate
 from qiskit.circuit.gate import Gate
 from qiskit.circuit.quantumregister import QuantumRegister
-from qiskit.circuit._utils import _compute_control_matrix
 from qiskit.qasm import pi
 from .t import TGate, TdgGate
 from .s import SGate, SdgGate
@@ -153,6 +152,18 @@ class CHGate(ControlledGate):
                 \end{pmatrix}
 
     """
+    # Define class constants. This saves future allocation time.
+    _sqrt2o2 = 1 / numpy.sqrt(2)
+    _matrix1 = numpy.array([[1, 0, 0, 0],
+                            [0, _sqrt2o2, 0, _sqrt2o2],
+                            [0, 0, 1, 0],
+                            [0, _sqrt2o2, 0, -_sqrt2o2]],
+                           dtype=complex)
+    _matrix0 = numpy.array([[_sqrt2o2, 0, _sqrt2o2, 0],
+                            [0, 1, 0, 0],
+                            [_sqrt2o2, 0, -_sqrt2o2, 0],
+                            [0, 0, 0, 1]],
+                           dtype=complex)
 
     def __init__(self, label=None, ctrl_state=None):
         """Create new CH gate."""
@@ -194,6 +205,7 @@ def inverse(self):
 
     def to_matrix(self):
         """Return a numpy.array for the CH gate."""
-        return _compute_control_matrix(self.base_gate.to_matrix(),
-                                       self.num_ctrl_qubits,
-                                       ctrl_state=self.ctrl_state)
+        if self.ctrl_state:
+            return self._matrix1
+        else:
+            return self._matrix0
diff --git a/qiskit/circuit/library/standard_gates/swap.py b/qiskit/circuit/library/standard_gates/swap.py
@@ -18,7 +18,6 @@
 from qiskit.circuit.controlledgate import ControlledGate
 from qiskit.circuit.gate import Gate
 from qiskit.circuit.quantumregister import QuantumRegister
-from qiskit.circuit._utils import _compute_control_matrix
 
 
 class SwapGate(Gate):
@@ -187,6 +186,23 @@ class CSwapGate(ControlledGate, metaclass=CSwapMeta):
         |0, b, c\rangle \rightarrow |0, b, c\rangle
         |1, b, c\rangle \rightarrow |1, c, b\rangle
     """
+    # Define class constants. This saves future allocation time.
+    _matrix1 = numpy.array([[1, 0, 0, 0, 0, 0, 0, 0],
+                            [0, 1, 0, 0, 0, 0, 0, 0],
+                            [0, 0, 1, 0, 0, 0, 0, 0],
+                            [0, 0, 0, 0, 0, 1, 0, 0],
+                            [0, 0, 0, 0, 1, 0, 0, 0],
+                            [0, 0, 0, 1, 0, 0, 0, 0],
+                            [0, 0, 0, 0, 0, 0, 1, 0],
+                            [0, 0, 0, 0, 0, 0, 0, 1]], dtype=complex)
+    _matrix0 = numpy.array([[1, 0, 0, 0, 0, 0, 0, 0],
+                            [0, 1, 0, 0, 0, 0, 0, 0],
+                            [0, 0, 0, 0, 1, 0, 0, 0],
+                            [0, 0, 0, 1, 0, 0, 0, 0],
+                            [0, 0, 1, 0, 0, 0, 0, 0],
+                            [0, 0, 0, 0, 0, 1, 0, 0],
+                            [0, 0, 0, 0, 0, 0, 1, 0],
+                            [0, 0, 0, 0, 0, 0, 0, 1]], dtype=complex)
 
     def __init__(self, label=None, ctrl_state=None):
         """Create new CSWAP gate."""
@@ -220,9 +236,10 @@ def inverse(self):
 
     def to_matrix(self):
         """Return a numpy.array for the Fredkin (CSWAP) gate."""
-        return _compute_control_matrix(self.base_gate.to_matrix(),
-                                       self.num_ctrl_qubits,
-                                       ctrl_state=self.ctrl_state)
+        if self.ctrl_state:
+            return self._matrix1
+        else:
+            return self._matrix0
 
 
 class FredkinGate(CSwapGate, metaclass=CSwapMeta):

diff --git a/qiskit/circuit/library/standard_gates/y.py b/qiskit/circuit/library/standard_gates/y.py
@@ -19,7 +19,6 @@
 from qiskit.circuit.controlledgate import ControlledGate
 from qiskit.circuit.gate import Gate
 from qiskit.circuit.quantumregister import QuantumRegister
-from qiskit.circuit._utils import _compute_control_matrix
 
 
 class YGate(Gate):
@@ -172,6 +171,15 @@ class CYGate(ControlledGate, metaclass=CYMeta):
                 \end{pmatrix}
 
     """
+    # Define class constants. This saves future allocation time.
+    _matrix1 = numpy.array([[1, 0, 0, 0],
+                            [0, 0, 0, -1j],
+                            [0, 0, 1, 0],
+                            [0, 1j, 0, 0]], dtype=complex)
+    _matrix0 = numpy.array([[0, 0, -1j, 0],
+                            [0, 1, 0, 0],
+                            [1j, 0, 0, 0],
+                            [0, 0, 0, 1]], dtype=complex)
 
     def __init__(self, label=None, ctrl_state=None):
         """Create new CY gate."""
@@ -202,9 +210,10 @@ def inverse(self):
 
     def to_matrix(self):
         """Return a numpy.array for the CY gate."""
-        return _compute_control_matrix(self.base_gate.to_matrix(),
-                                       self.num_ctrl_qubits,
-                                       ctrl_state=self.ctrl_state)
+        if self.ctrl_state:
+            return self._matrix1
+        else:
+            return self._matrix0
 
 
 class CyGate(CYGate, metaclass=CYMeta):