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Source code for qiskit.transpiler.layout

# 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.

"""
A two-ways dict to represent a layout.

Layout is the relation between virtual (qu)bits and physical (qu)bits.
Virtual (qu)bits are tuples, e.g. `(QuantumRegister(3, 'qr'), 2)` or simply `qr[2]`.
Physical (qu)bits are integers.
"""

from dataclasses import dataclass
from typing import Dict

from qiskit.circuit.quantumregister import Qubit, QuantumRegister
from qiskit.transpiler.exceptions import LayoutError
from qiskit.converters import isinstanceint


[docs]class Layout: """Two-ways dict to represent a Layout.""" __slots__ = ("_regs", "_p2v", "_v2p") def __init__(self, input_dict=None): """construct a Layout from a bijective dictionary, mapping virtual qubits to physical qubits""" self._regs = [] self._p2v = {} self._v2p = {} if input_dict is not None: if not isinstance(input_dict, dict): raise LayoutError("Layout constructor takes a dict") self.from_dict(input_dict) def __repr__(self): """Representation of a Layout""" str_list = [] for key, val in self._p2v.items(): str_list.append(f"{key}: {val},") if str_list: str_list[-1] = str_list[-1][:-1] return "Layout({\n" + "\n".join(str_list) + "\n})"
[docs] def from_dict(self, input_dict): """Populates a Layout from a dictionary. The dictionary must be a bijective mapping between virtual qubits (tuple) and physical qubits (int). Args: input_dict (dict): e.g.:: {(QuantumRegister(3, 'qr'), 0): 0, (QuantumRegister(3, 'qr'), 1): 1, (QuantumRegister(3, 'qr'), 2): 2} Can be written more concisely as follows: * virtual to physical:: {qr[0]: 0, qr[1]: 1, qr[2]: 2} * physical to virtual:: {0: qr[0], 1: qr[1], 2: qr[2]} """ for key, value in input_dict.items(): virtual, physical = Layout.order_based_on_type(key, value) self._p2v[physical] = virtual if virtual is None: continue self._v2p[virtual] = physical
[docs] @staticmethod def order_based_on_type(value1, value2): """decides which one is physical/virtual based on the type. Returns (virtual, physical)""" if isinstanceint(value1) and isinstance(value2, (Qubit, type(None))): physical = int(value1) virtual = value2 elif isinstanceint(value2) and isinstance(value1, (Qubit, type(None))): physical = int(value2) virtual = value1 else: raise LayoutError( "The map (%s -> %s) has to be a (Bit -> integer)" " or the other way around." % (type(value1), type(value2)) ) return virtual, physical
def __getitem__(self, item): if item in self._p2v: return self._p2v[item] if item in self._v2p: return self._v2p[item] raise KeyError(f"The item {item} does not exist in the Layout") def __contains__(self, item): return item in self._p2v or item in self._v2p def __setitem__(self, key, value): virtual, physical = Layout.order_based_on_type(key, value) self._set_type_checked_item(virtual, physical) def _set_type_checked_item(self, virtual, physical): old = self._v2p.pop(virtual, None) self._p2v.pop(old, None) old = self._p2v.pop(physical, None) self._v2p.pop(old, None) self._p2v[physical] = virtual if virtual is not None: self._v2p[virtual] = physical def __delitem__(self, key): if isinstance(key, int): del self._v2p[self._p2v[key]] del self._p2v[key] elif isinstance(key, Qubit): del self._p2v[self._v2p[key]] del self._v2p[key] else: raise LayoutError( "The key to remove should be of the form" " Qubit or integer) and %s was provided" % (type(key),) ) def __len__(self): return len(self._p2v) def __eq__(self, other): if isinstance(other, Layout): return self._p2v == other._p2v and self._v2p == other._v2p return False
[docs] def copy(self): """Returns a copy of a Layout instance.""" layout_copy = type(self)() layout_copy._regs = self._regs.copy() layout_copy._p2v = self._p2v.copy() layout_copy._v2p = self._v2p.copy() return layout_copy
[docs] def add(self, virtual_bit, physical_bit=None): """ Adds a map element between `bit` and `physical_bit`. If `physical_bit` is not defined, `bit` will be mapped to a new physical bit. Args: virtual_bit (tuple): A (qu)bit. For example, (QuantumRegister(3, 'qr'), 2). physical_bit (int): A physical bit. For example, 3. """ if physical_bit is None: if len(self._p2v) == 0: physical_bit = 0 else: max_physical = max(self._p2v) # Fill any gaps in the existing bits for physical_candidate in range(max_physical): if physical_candidate not in self._p2v: physical_bit = physical_candidate break # If there are no free bits in the allocated physical bits add new ones else: physical_bit = max_physical + 1 self[virtual_bit] = physical_bit
[docs] def add_register(self, reg): """Adds at the end physical_qubits that map each bit in reg. Args: reg (Register): A (qu)bit Register. For example, QuantumRegister(3, 'qr'). """ self._regs.append(reg) for bit in reg: if bit not in self: self.add(bit)
[docs] def get_registers(self): """ Returns the registers in the layout [QuantumRegister(2, 'qr0'), QuantumRegister(3, 'qr1')] Returns: Set: A set of Registers in the layout """ return set(self._regs)
[docs] def get_virtual_bits(self): """ Returns the dictionary where the keys are virtual (qu)bits and the values are physical (qu)bits. """ return self._v2p
[docs] def get_physical_bits(self): """ Returns the dictionary where the keys are physical (qu)bits and the values are virtual (qu)bits. """ return self._p2v
[docs] def swap(self, left, right): """Swaps the map between left and right. Args: left (tuple or int): Item to swap with right. right (tuple or int): Item to swap with left. Raises: LayoutError: If left and right have not the same type. """ if type(left) is not type(right): raise LayoutError("The method swap only works with elements of the same type.") temp = self[left] self[left] = self[right] self[right] = temp
[docs] def combine_into_edge_map(self, another_layout): """Combines self and another_layout into an "edge map". For example:: self another_layout resulting edge map qr_1 -> 0 0 <- q_2 qr_1 -> q_2 qr_2 -> 2 2 <- q_1 qr_2 -> q_1 qr_3 -> 3 3 <- q_0 qr_3 -> q_0 The edge map is used to compose dags via, for example, compose. Args: another_layout (Layout): The other layout to combine. Returns: dict: A "edge map". Raises: LayoutError: another_layout can be bigger than self, but not smaller. Otherwise, raises. """ edge_map = {} for virtual, physical in self._v2p.items(): if physical not in another_layout._p2v: raise LayoutError( "The wire_map_from_layouts() method does not support when the" " other layout (another_layout) is smaller." ) edge_map[virtual] = another_layout[physical] return edge_map
[docs] def reorder_bits(self, bits): """Given an ordered list of bits, reorder them according to this layout. The list of bits must exactly match the virtual bits in this layout. Args: bits (list[Bit]): the bits to reorder. Returns: List: ordered bits. """ order = [0] * len(bits) # the i-th bit is now sitting in position j for i, v in enumerate(bits): j = self[v] order[i] = j return order
[docs] @staticmethod def generate_trivial_layout(*regs): """Creates a trivial ("one-to-one") Layout with the registers and qubits in `regs`. Args: *regs (Registers, Qubits): registers and qubits to include in the layout. Returns: Layout: A layout with all the `regs` in the given order. """ layout = Layout() for reg in regs: if isinstance(reg, QuantumRegister): layout.add_register(reg) else: layout.add(reg) return layout
[docs] @staticmethod def from_intlist(int_list, *qregs): """Converts a list of integers to a Layout mapping virtual qubits (index of the list) to physical qubits (the list values). Args: int_list (list): A list of integers. *qregs (QuantumRegisters): The quantum registers to apply the layout to. Returns: Layout: The corresponding Layout object. Raises: LayoutError: Invalid input layout. """ if not all(isinstanceint(i) for i in int_list): raise LayoutError("Expected a list of ints") if len(int_list) != len(set(int_list)): raise LayoutError("Duplicate values not permitted; Layout is bijective.") num_qubits = sum(reg.size for reg in qregs) # Check if list is too short to cover all qubits if len(int_list) != num_qubits: raise LayoutError( f"Integer list length ({len(int_list)}) must equal number of qubits " f"in circuit ({num_qubits}): {int_list}." ) out = Layout() main_idx = 0 for qreg in qregs: for idx in range(qreg.size): out[qreg[idx]] = int_list[main_idx] main_idx += 1 out.add_register(qreg) if main_idx != len(int_list): for int_item in int_list[main_idx:]: out[int_item] = None return out
[docs] @staticmethod def from_qubit_list(qubit_list, *qregs): """ Populates a Layout from a list containing virtual qubits, Qubit or None. Args: qubit_list (list): e.g.: [qr[0], None, qr[2], qr[3]] *qregs (QuantumRegisters): The quantum registers to apply the layout to. Returns: Layout: the corresponding Layout object Raises: LayoutError: If the elements are not Qubit or None """ out = Layout() for physical, virtual in enumerate(qubit_list): if virtual is None: continue if isinstance(virtual, Qubit): if virtual in out._v2p: raise LayoutError("Duplicate values not permitted; Layout is bijective.") out[virtual] = physical else: raise LayoutError("The list should contain elements of the Bits or NoneTypes") for qreg in qregs: out.add_register(qreg) return out
@dataclass class TranspileLayout: """Layout attributes from output circuit from transpiler.""" initial_layout: Layout input_qubit_mapping: Dict[Qubit, int]