# -*- coding: utf-8 -*-
# This code is part of Qiskit.
#
# (C) Copyright IBM 2019.
#
# 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.
"""Evaluate how good the layout selection was.
No CX direction is considered.
Saves in `property_set['layout_score']` the sum of distances for each circuit CX.
The lower the number, the better the selection.
Therefore, 0 is a perfect layout selection.
"""
from qiskit.transpiler.basepasses import AnalysisPass
[docs]class Layout2qDistance(AnalysisPass):
"""Evaluate how good the layout selection was.
Saves in `property_set['layout_score']` (or the property name in property_name)
the sum of distances for each circuit CX.
The lower the number, the better the selection. Therefore, 0 is a perfect layout selection.
No CX direction is considered.
"""
def __init__(self, coupling_map, property_name='layout_score'):
"""Layout2qDistance initializer.
Args:
coupling_map (CouplingMap): Directed graph represented a coupling map.
property_name (str): The property name to save the score. Default: layout_score
"""
super().__init__()
self.coupling_map = coupling_map
self.property_name = property_name
[docs] def run(self, dag):
"""
Run the Layout2qDistance pass on `dag`.
Args:
dag (DAGCircuit): DAG to evaluate.
"""
layout = self.property_set["layout"]
if layout is None:
return
sum_distance = 0
for gate in dag.two_qubit_ops():
physical_q0 = layout[gate.qargs[0]]
physical_q1 = layout[gate.qargs[1]]
sum_distance += self.coupling_map.distance(physical_q0, physical_q1)-1
self.property_set[self.property_name] = sum_distance