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Código fuente para qiskit.transpiler.passes.layout.csp_layout

# 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.

"""A pass for choosing a Layout of a circuit onto a Coupling graph, as a
Constraint Satisfaction Problem. It tries to find a solution that fully
satisfy the circuit, i.e. no further swap is needed. If no solution is
found, no ``property_set['layout']`` is set.
"""
import random

from qiskit.transpiler.layout import Layout
from qiskit.transpiler.basepasses import AnalysisPass
from qiskit.utils import optionals as _optionals


[documentos]@_optionals.HAS_CONSTRAINT.require_in_instance class CSPLayout(AnalysisPass): """If possible, chooses a Layout as a CSP, using backtracking.""" def __init__( self, coupling_map, strict_direction=False, seed=None, call_limit=1000, time_limit=10 ): """If possible, chooses a Layout as a CSP, using backtracking. If not possible, does not set the layout property. In all the cases, the property `CSPLayout_stop_reason` will be added with one of the following values: * solution found: If a perfect layout was found. * nonexistent solution: If no perfect layout was found and every combination was checked. * call limit reached: If no perfect layout was found and the call limit was reached. * time limit reached: If no perfect layout was found and the time limit was reached. Args: coupling_map (Coupling): Directed graph representing a coupling map. strict_direction (bool): If True, considers the direction of the coupling map. Default is False. seed (int): Sets the seed of the PRNG. call_limit (int): Amount of times that ``constraint.RecursiveBacktrackingSolver.recursiveBacktracking`` will be called. None means no call limit. Default: 1000. time_limit (int): Amount of seconds that the pass will try to find a solution. None means no time limit. Default: 10 seconds. """ super().__init__() self.coupling_map = coupling_map self.strict_direction = strict_direction self.call_limit = call_limit self.time_limit = time_limit self.seed = seed
[documentos] def run(self, dag): """run the layout method""" qubits = dag.qubits cxs = set() from constraint import Problem, AllDifferentConstraint, RecursiveBacktrackingSolver from qiskit.transpiler.passes.layout._csp_custom_solver import CustomSolver for gate in dag.two_qubit_ops(): cxs.add((qubits.index(gate.qargs[0]), qubits.index(gate.qargs[1]))) edges = set(self.coupling_map.get_edges()) if self.time_limit is None and self.call_limit is None: solver = RecursiveBacktrackingSolver() else: solver = CustomSolver(call_limit=self.call_limit, time_limit=self.time_limit) variables = list(range(len(qubits))) variable_domains = list(self.coupling_map.physical_qubits) random.Random(self.seed).shuffle(variable_domains) problem = Problem(solver) problem.addVariables(variables, variable_domains) problem.addConstraint(AllDifferentConstraint()) # each wire is map to a single qubit if self.strict_direction: def constraint(control, target): return (control, target) in edges else: def constraint(control, target): return (control, target) in edges or (target, control) in edges for pair in cxs: problem.addConstraint(constraint, [pair[0], pair[1]]) solution = problem.getSolution() if solution is None: stop_reason = "nonexistent solution" if isinstance(solver, CustomSolver): if solver.time_current is not None and solver.time_current >= self.time_limit: stop_reason = "time limit reached" elif solver.call_current is not None and solver.call_current >= self.call_limit: stop_reason = "call limit reached" else: stop_reason = "solution found" self.property_set["layout"] = Layout({v: qubits[k] for k, v in solution.items()}) for reg in dag.qregs.values(): self.property_set["layout"].add_register(reg) self.property_set["CSPLayout_stop_reason"] = stop_reason