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Source code for qiskit.transpiler.passes.optimization.cx_cancellation

# 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.

"""Cancel back-to-back `cx` gates in dag."""

from qiskit.transpiler.basepasses import TransformationPass

[docs]class CXCancellation(TransformationPass): """Cancel back-to-back `cx` gates in dag."""
[docs] def run(self, dag): """Run the CXCancellation pass on `dag`. Args: dag (DAGCircuit): the directed acyclic graph to run on. Returns: DAGCircuit: Transformed DAG. """ cx_runs = dag.collect_runs(["cx"]) for cx_run in cx_runs: # Partition the cx_run into chunks with equal gate arguments partition = [] chunk = [] for i in range(len(cx_run) - 1): chunk.append(cx_run[i]) qargs0 = cx_run[i].qargs qargs1 = cx_run[i + 1].qargs if qargs0 != qargs1: partition.append(chunk) chunk = [] chunk.append(cx_run[-1]) partition.append(chunk) # Simplify each chunk in the partition for chunk in partition: if len(chunk) % 2 == 0: for n in chunk: dag.remove_op_node(n) else: for n in chunk[1:]: dag.remove_op_node(n) return dag

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