# Code source de qiskit.transpiler.passes.optimization.optimize_1q_decomposition

```
# This code is part of Qiskit.
#
# (C) Copyright IBM 2017, 2018.
#
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
#
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.
"""Optimize chains of single-qubit gates using Euler 1q decomposer"""
import copy
import logging
import warnings
import numpy as np
from qiskit.circuit.library.standard_gates import U3Gate
from qiskit.transpiler.basepasses import TransformationPass
from qiskit.quantum_info.synthesis import one_qubit_decompose
from qiskit.converters import circuit_to_dag
logger = logging.getLogger(__name__)
[docs]class Optimize1qGatesDecomposition(TransformationPass):
"""Optimize chains of single-qubit gates by combining them into a single gate."""
def __init__(self, basis=None):
"""Optimize1qGatesDecomposition initializer.
Args:
basis (list[str]): Basis gates to consider, e.g. `['u3', 'cx']`. For the effects
of this pass, the basis is the set intersection between the `basis` parameter
and the Euler basis.
"""
super().__init__()
self._target_basis = basis
self._decomposers = None
if basis:
self._decomposers = {}
basis_set = set(basis)
euler_basis_gates = one_qubit_decompose.ONE_QUBIT_EULER_BASIS_GATES
for euler_basis_name, gates in euler_basis_gates.items():
if set(gates).issubset(basis_set):
basis_copy = copy.copy(self._decomposers)
for base in basis_copy.keys():
# check if gates are a superset of another basis
if set(base).issubset(set(gates)):
# if so, remove that basis
del self._decomposers[base]
# check if the gates are a subset of another basis
elif set(gates).issubset(set(base)):
# if so, don't bother
break
# if not a subset, add it to the list
else:
self._decomposers[
tuple(gates)
] = one_qubit_decompose.OneQubitEulerDecomposer(euler_basis_name)
[docs] def run(self, dag):
"""Run the Optimize1qGatesDecomposition pass on `dag`.
Args:
dag (DAGCircuit): the DAG to be optimized.
Returns:
DAGCircuit: the optimized DAG.
"""
if self._decomposers is None:
logger.info("Skipping pass because no basis is set")
return dag
runs = dag.collect_1q_runs()
for run in runs:
# SPECIAL CASE: Don't bother to optimize single U3 gates which are in the basis set.
# The U3 decomposer is only going to emit a sequence of length 1 anyhow.
if "u3" in self._target_basis and len(run) == 1 and isinstance(run[0].op, U3Gate):
# Toss U3 gates equivalent to the identity; there we get off easy.
if np.allclose(run[0].op.to_matrix(), np.eye(2), 1e-15, 0):
dag.remove_op_node(run[0])
continue
# We might rewrite into lower `u`s if they're available.
if "u2" not in self._target_basis and "u1" not in self._target_basis:
continue
operator = run[0].op.to_matrix()
for gate in run[1:]:
operator = gate.op.to_matrix().dot(operator)
new_circs = {k: v._decompose(operator) for k, v in self._decomposers.items()}
if len(new_circs) > 0:
new_basis, new_circ = min(new_circs.items(), key=lambda x: len(x[1]))
# do we even have calibrations?
has_cals_p = dag.calibrations is not None and len(dag.calibrations) > 0
# is this run in the target set of this particular decomposer and also uncalibrated?
rewriteable_and_in_basis_p = all(
g.name in new_basis and (not has_cals_p or not dag.has_calibration_for(g))
for g in run
)
# does this run have uncalibrated gates?
uncalibrated_p = not has_cals_p or any(not dag.has_calibration_for(g) for g in run)
# does this run have gates not in the image of ._decomposers _and_ uncalibrated?
uncalibrated_and_not_basis_p = any(
g.name not in self._target_basis
and (not has_cals_p or not dag.has_calibration_for(g))
for g in run
)
if rewriteable_and_in_basis_p and len(run) < len(new_circ):
# NOTE: This is short-circuited on calibrated gates, which we're timid about
# reducing.
warnings.warn(
f"Resynthesized {run} and got {new_circ}, "
f"but the original was native and the new value is longer. This "
f"indicates an efficiency bug in synthesis. Please report it by "
f"opening an issue here: "
f"https://github.com/Qiskit/qiskit-terra/issues/new/choose",
stacklevel=2,
)
# if we're outside of the basis set, we're obligated to logically decompose.
# if we're outside of the set of gates for which we have physical definitions,
# then we _try_ to decompose, using the results if we see improvement.
# NOTE: Here we use circuit length as a weak proxy for "improvement"; in reality,
# we care about something more like fidelity at runtime, which would mean,
# e.g., a preference for `RZGate`s over `RXGate`s. In fact, users sometimes
# express a preference for a "canonical form" of a circuit, which may come in
# the form of some parameter values, also not visible at the level of circuit
# length. Since we don't have a framework for the caller to programmatically
# express what they want here, we include some special casing for particular
# gates which we've promised to normalize --- but this is fragile and should
# ultimately be done away with.
if (
uncalibrated_and_not_basis_p
or (uncalibrated_p and len(run) > len(new_circ))
or isinstance(run[0].op, U3Gate)
):
new_dag = circuit_to_dag(new_circ)
dag.substitute_node_with_dag(run[0], new_dag)
# Delete the other nodes in the run
for current_node in run[1:]:
dag.remove_op_node(current_node)
return dag
```