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Source code for qiskit.transpiler.layout

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# (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.
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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 qiskit.circuit.quantumregister import Qubit
from qiskit.transpiler.exceptions import LayoutError
from qiskit.converters import isinstanceint

[docs]class Layout(): """Two-ways dict to represent a Layout."""
[docs] def __init__(self, input_dict=None): """construct a Layout from a bijective dictionary, mapping virtual qubits to physical qubits""" 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("{k}: {v},".format(k=key, v=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('The item %s does not exist in the Layout' % (item,)) 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._p2v[key] del self._v2p[self._p2v[key]] elif isinstance(key, Qubit): del self._v2p[key] del self._p2v[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)
[docs] def copy(self): """Returns a copy of a Layout instance.""" layout_copy = type(self)() 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 (extending the length of the layout by one.) 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: physical_candidate = len(self) while physical_candidate in self._p2v: physical_candidate += 1 physical_bit = physical_candidate 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'). """ for bit in reg: self.add(bit)
[docs] def get_registers(self): """ Returns the registers in the layout [QuantumRegister(2, 'qr0'), QuantumRegister(3, 'qr1')] Returns: List: A list of Register in the layout """ return {bit.register for bit in self.get_virtual_bits()}
[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 = dict() for virtual, physical in self.get_virtual_bits().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 in `regs`. Args: *regs (Registers): registers to include in the layout. Returns: Layout: A layout with all the `regs` in the given order. """ layout = Layout() for reg in regs: layout.add_register(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('Integer list length must equal number of qubits in circuit.') 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 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): """ 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]] 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") return out

© Copyright 2020, Qiskit Development Team. Last updated on 2021/03/06.

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