# This code is part of Qiskit.
#
# (C) Copyright IBM 2017, 2021.
#
# 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.
"""
Object to represent a quantum circuit as a directed acyclic graph (DAG).
The nodes in the graph are either input/output nodes or operation nodes.
The edges correspond to qubits or bits in the circuit. A directed edge
from node A to node B means that the (qu)bit passes from the output of A
to the input of B. The object's methods allow circuits to be constructed,
composed, and modified. Some natural properties like depth can be computed
directly from the graph.
"""
from collections import OrderedDict, defaultdict, deque, namedtuple
import copy
import math
import warnings
from typing import Dict, Generator, Any, List
import numpy as np
import rustworkx as rx
from qiskit.circuit import (
ControlFlowOp,
ForLoopOp,
IfElseOp,
WhileLoopOp,
SwitchCaseOp,
_classical_resource_map,
)
from qiskit.circuit.controlflow import condition_resources, node_resources, CONTROL_FLOW_OP_NAMES
from qiskit.circuit.quantumregister import QuantumRegister, Qubit
from qiskit.circuit.classicalregister import ClassicalRegister, Clbit
from qiskit.circuit.gate import Gate
from qiskit.circuit.instruction import Instruction
from qiskit.circuit.parameterexpression import ParameterExpression
from qiskit.dagcircuit.exceptions import DAGCircuitError
from qiskit.dagcircuit.dagnode import DAGNode, DAGOpNode, DAGInNode, DAGOutNode
from qiskit.circuit.bit import Bit
BitLocations = namedtuple("BitLocations", ("index", "registers"))
[docs]class DAGCircuit:
"""
Quantum circuit as a directed acyclic graph.
There are 3 types of nodes in the graph: inputs, outputs, and operations.
The nodes are connected by directed edges that correspond to qubits and
bits.
"""
# pylint: disable=invalid-name
def __init__(self):
"""Create an empty circuit."""
# Circuit name. Generally, this corresponds to the name
# of the QuantumCircuit from which the DAG was generated.
self.name = None
# Circuit metadata
self.metadata = {}
# Cache of dag op node sort keys
self._key_cache = {}
# Set of wires (Register,idx) in the dag
self._wires = set()
# Map from wire (Register,idx) to input nodes of the graph
self.input_map = OrderedDict()
# Map from wire (Register,idx) to output nodes of the graph
self.output_map = OrderedDict()
# Directed multigraph whose nodes are inputs, outputs, or operations.
# Operation nodes have equal in- and out-degrees and carry
# additional data about the operation, including the argument order
# and parameter values.
# Input nodes have out-degree 1 and output nodes have in-degree 1.
# Edges carry wire labels (reg,idx) and each operation has
# corresponding in- and out-edges with the same wire labels.
self._multi_graph = rx.PyDAG()
# Map of qreg/creg name to Register object.
self.qregs = OrderedDict()
self.cregs = OrderedDict()
# List of Qubit/Clbit wires that the DAG acts on.
self.qubits: List[Qubit] = []
self.clbits: List[Clbit] = []
# Dictionary mapping of Qubit and Clbit instances to a tuple comprised of
# 0) corresponding index in dag.{qubits,clbits} and
# 1) a list of Register-int pairs for each Register containing the Bit and
# its index within that register.
self._qubit_indices: Dict[Qubit, BitLocations] = {}
self._clbit_indices: Dict[Clbit, BitLocations] = {}
self._global_phase = 0
self._calibrations = defaultdict(dict)
self._op_names = {}
self.duration = None
self.unit = "dt"
@property
def wires(self):
"""Return a list of the wires in order."""
return self.qubits + self.clbits
@property
def node_counter(self):
"""
Returns the number of nodes in the dag.
"""
return len(self._multi_graph)
@property
def global_phase(self):
"""Return the global phase of the circuit."""
return self._global_phase
@global_phase.setter
def global_phase(self, angle):
"""Set the global phase of the circuit.
Args:
angle (float, ParameterExpression)
"""
if isinstance(angle, ParameterExpression):
self._global_phase = angle
else:
# Set the phase to the [0, 2Ï€) interval
angle = float(angle)
if not angle:
self._global_phase = 0
else:
self._global_phase = angle % (2 * math.pi)
@property
def calibrations(self):
"""Return calibration dictionary.
The custom pulse definition of a given gate is of the form
{'gate_name': {(qubits, params): schedule}}
"""
return dict(self._calibrations)
@calibrations.setter
def calibrations(self, calibrations):
"""Set the circuit calibration data from a dictionary of calibration definition.
Args:
calibrations (dict): A dictionary of input in the format
{'gate_name': {(qubits, gate_params): schedule}}
"""
self._calibrations = defaultdict(dict, calibrations)
[docs] def add_calibration(self, gate, qubits, schedule, params=None):
"""Register a low-level, custom pulse definition for the given gate.
Args:
gate (Union[Gate, str]): Gate information.
qubits (Union[int, Tuple[int]]): List of qubits to be measured.
schedule (Schedule): Schedule information.
params (Optional[List[Union[float, Parameter]]]): A list of parameters.
Raises:
Exception: if the gate is of type string and params is None.
"""
def _format(operand):
try:
# Using float/complex value as a dict key is not good idea.
# This makes the mapping quite sensitive to the rounding error.
# However, the mechanism is already tied to the execution model (i.e. pulse gate)
# and we cannot easily update this rule.
# The same logic exists in QuantumCircuit.add_calibration.
evaluated = complex(operand)
if np.isreal(evaluated):
evaluated = float(evaluated.real)
if evaluated.is_integer():
evaluated = int(evaluated)
return evaluated
except TypeError:
# Unassigned parameter
return operand
if isinstance(gate, Gate):
params = gate.params
gate = gate.name
if params is not None:
params = tuple(map(_format, params))
else:
params = ()
self._calibrations[gate][(tuple(qubits), params)] = schedule
[docs] def has_calibration_for(self, node):
"""Return True if the dag has a calibration defined for the node operation. In this
case, the operation does not need to be translated to the device basis.
"""
if not self.calibrations or node.op.name not in self.calibrations:
return False
qubits = tuple(self.qubits.index(qubit) for qubit in node.qargs)
params = []
for p in node.op.params:
if isinstance(p, ParameterExpression) and not p.parameters:
params.append(float(p))
else:
params.append(p)
params = tuple(params)
return (qubits, params) in self.calibrations[node.op.name]
[docs] def remove_all_ops_named(self, opname):
"""Remove all operation nodes with the given name."""
for n in self.named_nodes(opname):
self.remove_op_node(n)
[docs] def add_qubits(self, qubits):
"""Add individual qubit wires."""
if any(not isinstance(qubit, Qubit) for qubit in qubits):
raise DAGCircuitError("not a Qubit instance.")
duplicate_qubits = set(self.qubits).intersection(qubits)
if duplicate_qubits:
raise DAGCircuitError("duplicate qubits %s" % duplicate_qubits)
for qubit in qubits:
self.qubits.append(qubit)
self._qubit_indices[qubit] = BitLocations(len(self.qubits) - 1, [])
self._add_wire(qubit)
[docs] def add_clbits(self, clbits):
"""Add individual clbit wires."""
if any(not isinstance(clbit, Clbit) for clbit in clbits):
raise DAGCircuitError("not a Clbit instance.")
duplicate_clbits = set(self.clbits).intersection(clbits)
if duplicate_clbits:
raise DAGCircuitError("duplicate clbits %s" % duplicate_clbits)
for clbit in clbits:
self.clbits.append(clbit)
self._clbit_indices[clbit] = BitLocations(len(self.clbits) - 1, [])
self._add_wire(clbit)
[docs] def add_qreg(self, qreg):
"""Add all wires in a quantum register."""
if not isinstance(qreg, QuantumRegister):
raise DAGCircuitError("not a QuantumRegister instance.")
if qreg.name in self.qregs:
raise DAGCircuitError("duplicate register %s" % qreg.name)
self.qregs[qreg.name] = qreg
existing_qubits = set(self.qubits)
for j in range(qreg.size):
if qreg[j] in self._qubit_indices:
self._qubit_indices[qreg[j]].registers.append((qreg, j))
if qreg[j] not in existing_qubits:
self.qubits.append(qreg[j])
self._qubit_indices[qreg[j]] = BitLocations(
len(self.qubits) - 1, registers=[(qreg, j)]
)
self._add_wire(qreg[j])
[docs] def add_creg(self, creg):
"""Add all wires in a classical register."""
if not isinstance(creg, ClassicalRegister):
raise DAGCircuitError("not a ClassicalRegister instance.")
if creg.name in self.cregs:
raise DAGCircuitError("duplicate register %s" % creg.name)
self.cregs[creg.name] = creg
existing_clbits = set(self.clbits)
for j in range(creg.size):
if creg[j] in self._clbit_indices:
self._clbit_indices[creg[j]].registers.append((creg, j))
if creg[j] not in existing_clbits:
self.clbits.append(creg[j])
self._clbit_indices[creg[j]] = BitLocations(
len(self.clbits) - 1, registers=[(creg, j)]
)
self._add_wire(creg[j])
def _add_wire(self, wire):
"""Add a qubit or bit to the circuit.
Args:
wire (Bit): the wire to be added
This adds a pair of in and out nodes connected by an edge.
Raises:
DAGCircuitError: if trying to add duplicate wire
"""
if wire not in self._wires:
self._wires.add(wire)
inp_node = DAGInNode(wire=wire)
outp_node = DAGOutNode(wire=wire)
input_map_id, output_map_id = self._multi_graph.add_nodes_from([inp_node, outp_node])
inp_node._node_id = input_map_id
outp_node._node_id = output_map_id
self.input_map[wire] = inp_node
self.output_map[wire] = outp_node
self._multi_graph.add_edge(inp_node._node_id, outp_node._node_id, wire)
else:
raise DAGCircuitError(f"duplicate wire {wire}")
[docs] def find_bit(self, bit: Bit) -> BitLocations:
"""
Finds locations in the circuit, by mapping the Qubit and Clbit to positional index
BitLocations is defined as: BitLocations = namedtuple("BitLocations", ("index", "registers"))
Args:
bit (Bit): The bit to locate.
Returns:
namedtuple(int, List[Tuple(Register, int)]): A 2-tuple. The first element (``index``)
contains the index at which the ``Bit`` can be found (in either
:obj:`~DAGCircuit.qubits`, :obj:`~DAGCircuit.clbits`, depending on its
type). The second element (``registers``) is a list of ``(register, index)``
pairs with an entry for each :obj:`~Register` in the circuit which contains the
:obj:`~Bit` (and the index in the :obj:`~Register` at which it can be found).
Raises:
DAGCircuitError: If the supplied :obj:`~Bit` was of an unknown type.
DAGCircuitError: If the supplied :obj:`~Bit` could not be found on the circuit.
"""
try:
if isinstance(bit, Qubit):
return self._qubit_indices[bit]
elif isinstance(bit, Clbit):
return self._clbit_indices[bit]
else:
raise DAGCircuitError(f"Could not locate bit of unknown type: {type(bit)}")
except KeyError as err:
raise DAGCircuitError(
f"Could not locate provided bit: {bit}. Has it been added to the DAGCircuit?"
) from err
[docs] def remove_clbits(self, *clbits):
"""
Remove classical bits from the circuit. All bits MUST be idle.
Any registers with references to at least one of the specified bits will
also be removed.
Args:
clbits (List[Clbit]): The bits to remove.
Raises:
DAGCircuitError: a clbit is not a :obj:`.Clbit`, is not in the circuit,
or is not idle.
"""
if any(not isinstance(clbit, Clbit) for clbit in clbits):
raise DAGCircuitError(
"clbits not of type Clbit: %s" % [b for b in clbits if not isinstance(b, Clbit)]
)
clbits = set(clbits)
unknown_clbits = clbits.difference(self.clbits)
if unknown_clbits:
raise DAGCircuitError("clbits not in circuit: %s" % unknown_clbits)
busy_clbits = {bit for bit in clbits if not self._is_wire_idle(bit)}
if busy_clbits:
raise DAGCircuitError("clbits not idle: %s" % busy_clbits)
# remove any references to bits
cregs_to_remove = {creg for creg in self.cregs.values() if not clbits.isdisjoint(creg)}
self.remove_cregs(*cregs_to_remove)
for clbit in clbits:
self._remove_idle_wire(clbit)
self.clbits.remove(clbit)
del self._clbit_indices[clbit]
# Update the indices of remaining clbits
for i, clbit in enumerate(self.clbits):
self._clbit_indices[clbit] = self._clbit_indices[clbit]._replace(index=i)
[docs] def remove_cregs(self, *cregs):
"""
Remove classical registers from the circuit, leaving underlying bits
in place.
Raises:
DAGCircuitError: a creg is not a ClassicalRegister, or is not in
the circuit.
"""
if any(not isinstance(creg, ClassicalRegister) for creg in cregs):
raise DAGCircuitError(
"cregs not of type ClassicalRegister: %s"
% [r for r in cregs if not isinstance(r, ClassicalRegister)]
)
unknown_cregs = set(cregs).difference(self.cregs.values())
if unknown_cregs:
raise DAGCircuitError("cregs not in circuit: %s" % unknown_cregs)
for creg in cregs:
del self.cregs[creg.name]
for j in range(creg.size):
bit = creg[j]
bit_position = self._clbit_indices[bit]
bit_position.registers.remove((creg, j))
[docs] def remove_qubits(self, *qubits):
"""
Remove quantum bits from the circuit. All bits MUST be idle.
Any registers with references to at least one of the specified bits will
also be removed.
Args:
qubits (List[Qubit]): The bits to remove.
Raises:
DAGCircuitError: a qubit is not a :obj:`.Qubit`, is not in the circuit,
or is not idle.
"""
if any(not isinstance(qubit, Qubit) for qubit in qubits):
raise DAGCircuitError(
"qubits not of type Qubit: %s" % [b for b in qubits if not isinstance(b, Qubit)]
)
qubits = set(qubits)
unknown_qubits = qubits.difference(self.qubits)
if unknown_qubits:
raise DAGCircuitError("qubits not in circuit: %s" % unknown_qubits)
busy_qubits = {bit for bit in qubits if not self._is_wire_idle(bit)}
if busy_qubits:
raise DAGCircuitError("qubits not idle: %s" % busy_qubits)
# remove any references to bits
qregs_to_remove = {qreg for qreg in self.qregs.values() if not qubits.isdisjoint(qreg)}
self.remove_qregs(*qregs_to_remove)
for qubit in qubits:
self._remove_idle_wire(qubit)
self.qubits.remove(qubit)
del self._qubit_indices[qubit]
# Update the indices of remaining qubits
for i, qubit in enumerate(self.qubits):
self._qubit_indices[qubit] = self._qubit_indices[qubit]._replace(index=i)
[docs] def remove_qregs(self, *qregs):
"""
Remove classical registers from the circuit, leaving underlying bits
in place.
Raises:
DAGCircuitError: a qreg is not a QuantumRegister, or is not in
the circuit.
"""
if any(not isinstance(qreg, QuantumRegister) for qreg in qregs):
raise DAGCircuitError(
"qregs not of type QuantumRegister: %s"
% [r for r in qregs if not isinstance(r, QuantumRegister)]
)
unknown_qregs = set(qregs).difference(self.qregs.values())
if unknown_qregs:
raise DAGCircuitError("qregs not in circuit: %s" % unknown_qregs)
for qreg in qregs:
del self.qregs[qreg.name]
for j in range(qreg.size):
bit = qreg[j]
bit_position = self._qubit_indices[bit]
bit_position.registers.remove((qreg, j))
def _is_wire_idle(self, wire):
"""Check if a wire is idle.
Args:
wire (Bit): a wire in the circuit.
Returns:
bool: true if the wire is idle, false otherwise.
Raises:
DAGCircuitError: the wire is not in the circuit.
"""
if wire not in self._wires:
raise DAGCircuitError("wire %s not in circuit" % wire)
try:
child = next(self.successors(self.input_map[wire]))
except StopIteration as e:
raise DAGCircuitError(
"Invalid dagcircuit input node %s has no output" % self.input_map[wire]
) from e
return child is self.output_map[wire]
def _remove_idle_wire(self, wire):
"""Remove an idle qubit or bit from the circuit.
Args:
wire (Bit): the wire to be removed, which MUST be idle.
"""
inp_node = self.input_map[wire]
oup_node = self.output_map[wire]
self._multi_graph.remove_node(inp_node._node_id)
self._multi_graph.remove_node(oup_node._node_id)
self._wires.remove(wire)
del self.input_map[wire]
del self.output_map[wire]
def _check_condition(self, name, condition):
"""Verify that the condition is valid.
Args:
name (string): used for error reporting
condition (tuple or None): a condition tuple (ClassicalRegister, int) or (Clbit, bool)
Raises:
DAGCircuitError: if conditioning on an invalid register
"""
if condition is None:
return
resources = condition_resources(condition)
for creg in resources.cregs:
if creg.name not in self.cregs:
raise DAGCircuitError(f"invalid creg in condition for {name}")
if not set(resources.clbits).issubset(self.clbits):
raise DAGCircuitError(f"invalid clbits in condition for {name}")
def _check_bits(self, args, amap):
"""Check the values of a list of (qu)bit arguments.
For each element of args, check that amap contains it.
Args:
args (list[Bit]): the elements to be checked
amap (dict): a dictionary keyed on Qubits/Clbits
Raises:
DAGCircuitError: if a qubit is not contained in amap
"""
# Check for each wire
for wire in args:
if wire not in amap:
raise DAGCircuitError(f"(qu)bit {wire} not found in {amap}")
@staticmethod
def _bits_in_operation(operation):
"""Return an iterable over the classical bits that are inherent to an instruction. This
includes a `condition`, or the `target` of a :class:`.ControlFlowOp`.
Args:
instruction: the :class:`~.circuit.Instruction` instance for a node.
Returns:
Iterable[Clbit]: the :class:`.Clbit`\\ s involved.
"""
# If updating this, also update the fast-path checker `DAGCirucit._operation_may_have_bits`.
if (condition := getattr(operation, "condition", None)) is not None:
yield from condition_resources(condition).clbits
if isinstance(operation, SwitchCaseOp):
target = operation.target
if isinstance(target, Clbit):
yield target
elif isinstance(target, ClassicalRegister):
yield from target
else:
yield from node_resources(target).clbits
@staticmethod
def _operation_may_have_bits(operation) -> bool:
"""Return whether a given :class:`.Operation` may contain any :class:`.Clbit` instances
in itself (e.g. a control-flow operation).
Args:
operation (qiskit.circuit.Operation): the operation to check.
"""
# This is separate to `_bits_in_operation` because most of the time there won't be any bits,
# so we want a fast path to be able to skip creating and testing a generator for emptiness.
#
# If updating this, also update `DAGCirucit._bits_in_operation`.
return getattr(operation, "condition", None) is not None or isinstance(
operation, SwitchCaseOp
)
def _increment_op(self, op):
if op.name in self._op_names:
self._op_names[op.name] += 1
else:
self._op_names[op.name] = 1
def _decrement_op(self, op):
if self._op_names[op.name] == 1:
del self._op_names[op.name]
else:
self._op_names[op.name] -= 1
[docs] def copy_empty_like(self):
"""Return a copy of self with the same structure but empty.
That structure includes:
* name and other metadata
* global phase
* duration
* all the qubits and clbits, including the registers.
Returns:
DAGCircuit: An empty copy of self.
"""
target_dag = DAGCircuit()
target_dag.name = self.name
target_dag._global_phase = self._global_phase
target_dag.duration = self.duration
target_dag.unit = self.unit
target_dag.metadata = self.metadata
target_dag._key_cache = self._key_cache
target_dag.add_qubits(self.qubits)
target_dag.add_clbits(self.clbits)
for qreg in self.qregs.values():
target_dag.add_qreg(qreg)
for creg in self.cregs.values():
target_dag.add_creg(creg)
return target_dag
[docs] def apply_operation_back(self, op, qargs=(), cargs=(), *, check=True):
"""Apply an operation to the output of the circuit.
Args:
op (qiskit.circuit.Operation): the operation associated with the DAG node
qargs (tuple[Qubit]): qubits that op will be applied to
cargs (tuple[Clbit]): cbits that op will be applied to
check (bool): If ``True`` (default), this function will enforce that the
:class:`.DAGCircuit` data-structure invariants are maintained (all ``qargs`` are
:class:`.Qubit`\\ s, all are in the DAG, etc). If ``False``, the caller *must*
uphold these invariants itself, but the cost of several checks will be skipped.
This is most useful when building a new DAG from a source of known-good nodes.
Returns:
DAGOpNode: the node for the op that was added to the dag
Raises:
DAGCircuitError: if a leaf node is connected to multiple outputs
"""
if qargs is None:
_warn_none_args()
qargs = ()
else:
qargs = tuple(qargs)
if cargs is None:
_warn_none_args()
cargs = ()
else:
cargs = tuple(cargs)
if self._operation_may_have_bits(op):
# This is the slow path; most of the time, this won't happen.
all_cbits = set(self._bits_in_operation(op)).union(cargs)
else:
all_cbits = cargs
if check:
self._check_condition(op.name, getattr(op, "condition", None))
self._check_bits(qargs, self.output_map)
self._check_bits(all_cbits, self.output_map)
node = DAGOpNode(op=op, qargs=qargs, cargs=cargs, dag=self)
node._node_id = self._multi_graph.add_node(node)
self._increment_op(op)
# Add new in-edges from predecessors of the output nodes to the
# operation node while deleting the old in-edges of the output nodes
# and adding new edges from the operation node to each output node
self._multi_graph.insert_node_on_in_edges_multiple(
node._node_id,
[self.output_map[bit]._node_id for bits in (qargs, all_cbits) for bit in bits],
)
return node
[docs] def apply_operation_front(self, op, qargs=(), cargs=(), *, check=True):
"""Apply an operation to the input of the circuit.
Args:
op (qiskit.circuit.Operation): the operation associated with the DAG node
qargs (tuple[Qubit]): qubits that op will be applied to
cargs (tuple[Clbit]): cbits that op will be applied to
check (bool): If ``True`` (default), this function will enforce that the
:class:`.DAGCircuit` data-structure invariants are maintained (all ``qargs`` are
:class:`.Qubit`\\ s, all are in the DAG, etc). If ``False``, the caller *must*
uphold these invariants itself, but the cost of several checks will be skipped.
This is most useful when building a new DAG from a source of known-good nodes.
Returns:
DAGOpNode: the node for the op that was added to the dag
Raises:
DAGCircuitError: if initial nodes connected to multiple out edges
"""
if qargs is None:
_warn_none_args()
qargs = ()
else:
qargs = tuple(qargs)
if cargs is None:
_warn_none_args()
cargs = ()
else:
cargs = tuple(cargs)
if self._operation_may_have_bits(op):
# This is the slow path; most of the time, this won't happen.
all_cbits = set(self._bits_in_operation(op)).union(cargs)
else:
all_cbits = cargs
if check:
self._check_condition(op.name, getattr(op, "condition", None))
self._check_bits(qargs, self.input_map)
self._check_bits(all_cbits, self.input_map)
node = DAGOpNode(op=op, qargs=qargs, cargs=cargs, dag=self)
node._node_id = self._multi_graph.add_node(node)
self._increment_op(op)
# Add new out-edges to successors of the input nodes from the
# operation node while deleting the old out-edges of the input nodes
# and adding new edges to the operation node from each input node
self._multi_graph.insert_node_on_out_edges_multiple(
node._node_id,
[self.input_map[bit]._node_id for bits in (qargs, all_cbits) for bit in bits],
)
return node
[docs] def compose(self, other, qubits=None, clbits=None, front=False, inplace=True):
"""Compose the ``other`` circuit onto the output of this circuit.
A subset of input wires of ``other`` are mapped
to a subset of output wires of this circuit.
``other`` can be narrower or of equal width to ``self``.
Args:
other (DAGCircuit): circuit to compose with self
qubits (list[Qubit|int]): qubits of self to compose onto.
clbits (list[Clbit|int]): clbits of self to compose onto.
front (bool): If True, front composition will be performed (not implemented yet)
inplace (bool): If True, modify the object. Otherwise return composed circuit.
Returns:
DAGCircuit: the composed dag (returns None if inplace==True).
Raises:
DAGCircuitError: if ``other`` is wider or there are duplicate edge mappings.
"""
if front:
raise DAGCircuitError("Front composition not supported yet.")
if len(other.qubits) > len(self.qubits) or len(other.clbits) > len(self.clbits):
raise DAGCircuitError(
"Trying to compose with another DAGCircuit which has more 'in' edges."
)
# number of qubits and clbits must match number in circuit or None
identity_qubit_map = dict(zip(other.qubits, self.qubits))
identity_clbit_map = dict(zip(other.clbits, self.clbits))
if qubits is None:
qubit_map = identity_qubit_map
elif len(qubits) != len(other.qubits):
raise DAGCircuitError(
"Number of items in qubits parameter does not"
" match number of qubits in the circuit."
)
else:
qubit_map = {
other.qubits[i]: (self.qubits[q] if isinstance(q, int) else q)
for i, q in enumerate(qubits)
}
if clbits is None:
clbit_map = identity_clbit_map
elif len(clbits) != len(other.clbits):
raise DAGCircuitError(
"Number of items in clbits parameter does not"
" match number of clbits in the circuit."
)
else:
clbit_map = {
other.clbits[i]: (self.clbits[c] if isinstance(c, int) else c)
for i, c in enumerate(clbits)
}
edge_map = {**qubit_map, **clbit_map} or None
# if no edge_map, try to do a 1-1 mapping in order
if edge_map is None:
edge_map = {**identity_qubit_map, **identity_clbit_map}
# Check the edge_map for duplicate values
if len(set(edge_map.values())) != len(edge_map):
raise DAGCircuitError("duplicates in wire_map")
# Compose
if inplace:
dag = self
else:
dag = copy.deepcopy(self)
dag.global_phase += other.global_phase
for gate, cals in other.calibrations.items():
dag._calibrations[gate].update(cals)
# Ensure that the error raised here is a `DAGCircuitError` for backwards compatiblity.
def _reject_new_register(reg):
raise DAGCircuitError(f"No register with '{reg.bits}' to map this expression onto.")
variable_mapper = _classical_resource_map.VariableMapper(
dag.cregs.values(), edge_map, _reject_new_register
)
for nd in other.topological_nodes():
if isinstance(nd, DAGInNode):
# if in edge_map, get new name, else use existing name
m_wire = edge_map.get(nd.wire, nd.wire)
# the mapped wire should already exist
if m_wire not in dag.output_map:
raise DAGCircuitError(
"wire %s[%d] not in self" % (m_wire.register.name, m_wire.index)
)
if nd.wire not in other._wires:
raise DAGCircuitError(
"inconsistent wire type for %s[%d] in other"
% (nd.register.name, nd.wire.index)
)
elif isinstance(nd, DAGOutNode):
# ignore output nodes
pass
elif isinstance(nd, DAGOpNode):
m_qargs = [edge_map.get(x, x) for x in nd.qargs]
m_cargs = [edge_map.get(x, x) for x in nd.cargs]
op = nd.op.copy()
if (condition := getattr(op, "condition", None)) is not None:
if not isinstance(op, ControlFlowOp):
op = op.c_if(*variable_mapper.map_condition(condition, allow_reorder=True))
else:
op.condition = variable_mapper.map_condition(condition, allow_reorder=True)
elif isinstance(op, SwitchCaseOp):
op.target = variable_mapper.map_target(op.target)
dag.apply_operation_back(op, m_qargs, m_cargs, check=False)
else:
raise DAGCircuitError("bad node type %s" % type(nd))
if not inplace:
return dag
else:
return None
[docs] def reverse_ops(self):
"""Reverse the operations in the ``self`` circuit.
Returns:
DAGCircuit: the reversed dag.
"""
# TODO: speed up
# pylint: disable=cyclic-import
from qiskit.converters import dag_to_circuit, circuit_to_dag
qc = dag_to_circuit(self)
reversed_qc = qc.reverse_ops()
reversed_dag = circuit_to_dag(reversed_qc)
return reversed_dag
[docs] def idle_wires(self, ignore=None):
"""Return idle wires.
Args:
ignore (list(str)): List of node names to ignore. Default: []
Yields:
Bit: Bit in idle wire.
Raises:
DAGCircuitError: If the DAG is invalid
"""
if ignore is None:
ignore = set()
ignore_set = set(ignore)
for wire in self._wires:
if not ignore:
if self._is_wire_idle(wire):
yield wire
else:
for node in self.nodes_on_wire(wire, only_ops=True):
if node.op.name not in ignore_set:
# If we found an op node outside of ignore we can stop iterating over the wire
break
else:
yield wire
[docs] def size(self, *, recurse: bool = False):
"""Return the number of operations. If there is control flow present, this count may only
be an estimate, as the complete control-flow path cannot be statically known.
Args:
recurse: if ``True``, then recurse into control-flow operations. For loops with
known-length iterators are counted unrolled. If-else blocks sum both of the two
branches. While loops are counted as if the loop body runs once only. Defaults to
``False`` and raises :class:`.DAGCircuitError` if any control flow is present, to
avoid silently returning a mostly meaningless number.
Returns:
int: the circuit size
Raises:
DAGCircuitError: if an unknown :class:`.ControlFlowOp` is present in a call with
``recurse=True``, or any control flow is present in a non-recursive call.
"""
length = len(self._multi_graph) - 2 * len(self._wires)
if not recurse:
if any(x in self._op_names for x in CONTROL_FLOW_OP_NAMES):
raise DAGCircuitError(
"Size with control flow is ambiguous."
" You may use `recurse=True` to get a result,"
" but see this method's documentation for the meaning of this."
)
return length
# pylint: disable=cyclic-import
from qiskit.converters import circuit_to_dag
for node in self.op_nodes(ControlFlowOp):
if isinstance(node.op, ForLoopOp):
indexset = node.op.params[0]
inner = len(indexset) * circuit_to_dag(node.op.blocks[0]).size(recurse=True)
elif isinstance(node.op, WhileLoopOp):
inner = circuit_to_dag(node.op.blocks[0]).size(recurse=True)
elif isinstance(node.op, (IfElseOp, SwitchCaseOp)):
inner = sum(circuit_to_dag(block).size(recurse=True) for block in node.op.blocks)
else:
raise DAGCircuitError(f"unknown control-flow type: '{node.op.name}'")
# Replace the "1" for the node itself with the actual count.
length += inner - 1
return length
[docs] def depth(self, *, recurse: bool = False):
"""Return the circuit depth. If there is control flow present, this count may only be an
estimate, as the complete control-flow path cannot be statically known.
Args:
recurse: if ``True``, then recurse into control-flow operations. For loops
with known-length iterators are counted as if the loop had been manually unrolled
(*i.e.* with each iteration of the loop body written out explicitly).
If-else blocks take the longer case of the two branches. While loops are counted as
if the loop body runs once only. Defaults to ``False`` and raises
:class:`.DAGCircuitError` if any control flow is present, to avoid silently
returning a nonsensical number.
Returns:
int: the circuit depth
Raises:
DAGCircuitError: if not a directed acyclic graph
DAGCircuitError: if unknown control flow is present in a recursive call, or any control
flow is present in a non-recursive call.
"""
if recurse:
from qiskit.converters import circuit_to_dag # pylint: disable=cyclic-import
node_lookup = {}
for node in self.op_nodes(ControlFlowOp):
weight = len(node.op.params[0]) if isinstance(node.op, ForLoopOp) else 1
if weight == 0:
node_lookup[node._node_id] = 0
else:
node_lookup[node._node_id] = weight * max(
circuit_to_dag(block).depth(recurse=True) for block in node.op.blocks
)
def weight_fn(_source, target, _edge):
return node_lookup.get(target, 1)
else:
if any(x in self._op_names for x in CONTROL_FLOW_OP_NAMES):
raise DAGCircuitError(
"Depth with control flow is ambiguous."
" You may use `recurse=True` to get a result,"
" but see this method's documentation for the meaning of this."
)
weight_fn = None
try:
depth = rx.dag_longest_path_length(self._multi_graph, weight_fn) - 1
except rx.DAGHasCycle as ex:
raise DAGCircuitError("not a DAG") from ex
return depth if depth >= 0 else 0
[docs] def width(self):
"""Return the total number of qubits + clbits used by the circuit.
This function formerly returned the number of qubits by the calculation
return len(self._wires) - self.num_clbits()
but was changed by issue #2564 to return number of qubits + clbits
with the new function DAGCircuit.num_qubits replacing the former
semantic of DAGCircuit.width().
"""
return len(self._wires)
[docs] def num_qubits(self):
"""Return the total number of qubits used by the circuit.
num_qubits() replaces former use of width().
DAGCircuit.width() now returns qubits + clbits for
consistency with Circuit.width() [qiskit-terra #2564].
"""
return len(self.qubits)
[docs] def num_clbits(self):
"""Return the total number of classical bits used by the circuit."""
return len(self.clbits)
[docs] def num_tensor_factors(self):
"""Compute how many components the circuit can decompose into."""
return rx.number_weakly_connected_components(self._multi_graph)
def __eq__(self, other):
# Try to convert to float, but in case of unbound ParameterExpressions
# a TypeError will be raise, fallback to normal equality in those
# cases
try:
self_phase = float(self.global_phase)
other_phase = float(other.global_phase)
if (
abs((self_phase - other_phase + np.pi) % (2 * np.pi) - np.pi) > 1.0e-10
): # TODO: atol?
return False
except TypeError:
if self.global_phase != other.global_phase:
return False
if self.calibrations != other.calibrations:
return False
self_bit_indices = {bit: idx for idx, bit in enumerate(self.qubits + self.clbits)}
other_bit_indices = {bit: idx for idx, bit in enumerate(other.qubits + other.clbits)}
self_qreg_indices = {
regname: [self_bit_indices[bit] for bit in reg] for regname, reg in self.qregs.items()
}
self_creg_indices = {
regname: [self_bit_indices[bit] for bit in reg] for regname, reg in self.cregs.items()
}
other_qreg_indices = {
regname: [other_bit_indices[bit] for bit in reg] for regname, reg in other.qregs.items()
}
other_creg_indices = {
regname: [other_bit_indices[bit] for bit in reg] for regname, reg in other.cregs.items()
}
if self_qreg_indices != other_qreg_indices or self_creg_indices != other_creg_indices:
return False
def node_eq(node_self, node_other):
return DAGNode.semantic_eq(node_self, node_other, self_bit_indices, other_bit_indices)
return rx.is_isomorphic_node_match(self._multi_graph, other._multi_graph, node_eq)
[docs] def topological_nodes(self, key=None):
"""
Yield nodes in topological order.
Args:
key (Callable): A callable which will take a DAGNode object and
return a string sort key. If not specified the
:attr:`~qiskit.dagcircuit.DAGNode.sort_key` attribute will be
used as the sort key for each node.
Returns:
generator(DAGOpNode, DAGInNode, or DAGOutNode): node in topological order
"""
def _key(x):
return x.sort_key
if key is None:
key = _key
return iter(rx.lexicographical_topological_sort(self._multi_graph, key=key))
[docs] def topological_op_nodes(self, key=None) -> Generator[DAGOpNode, Any, Any]:
"""
Yield op nodes in topological order.
Allowed to pass in specific key to break ties in top order
Args:
key (Callable): A callable which will take a DAGNode object and
return a string sort key. If not specified the
:attr:`~qiskit.dagcircuit.DAGNode.sort_key` attribute will be
used as the sort key for each node.
Returns:
generator(DAGOpNode): op node in topological order
"""
return (nd for nd in self.topological_nodes(key) if isinstance(nd, DAGOpNode))
[docs] def replace_block_with_op(self, node_block, op, wire_pos_map, cycle_check=True):
"""Replace a block of nodes with a single node.
This is used to consolidate a block of DAGOpNodes into a single
operation. A typical example is a block of gates being consolidated
into a single ``UnitaryGate`` representing the unitary matrix of the
block.
Args:
node_block (List[DAGNode]): A list of dag nodes that represents the
node block to be replaced
op (qiskit.circuit.Operation): The operation to replace the
block with
wire_pos_map (Dict[Bit, int]): The dictionary mapping the bits to their positions in the
output ``qargs`` or ``cargs``. This is necessary to reconstruct the arg order over
multiple gates in the combined single op node. If a :class:`.Bit` is not in the
dictionary, it will not be added to the args; this can be useful when dealing with
control-flow operations that have inherent bits in their ``condition`` or ``target``
fields.
cycle_check (bool): When set to True this method will check that
replacing the provided ``node_block`` with a single node
would introduce a cycle (which would invalidate the
``DAGCircuit``) and will raise a ``DAGCircuitError`` if a cycle
would be introduced. This checking comes with a run time
penalty. If you can guarantee that your input ``node_block`` is
a contiguous block and won't introduce a cycle when it's
contracted to a single node, this can be set to ``False`` to
improve the runtime performance of this method.
Raises:
DAGCircuitError: if ``cycle_check`` is set to ``True`` and replacing
the specified block introduces a cycle or if ``node_block`` is
empty.
Returns:
DAGOpNode: The op node that replaces the block.
"""
block_qargs = set()
block_cargs = set()
block_ids = [x._node_id for x in node_block]
# If node block is empty return early
if not node_block:
raise DAGCircuitError("Can't replace an empty node_block")
for nd in node_block:
block_qargs |= set(nd.qargs)
block_cargs |= set(nd.cargs)
if (condition := getattr(nd.op, "condition", None)) is not None:
block_cargs.update(condition_resources(condition).clbits)
elif isinstance(nd.op, SwitchCaseOp):
if isinstance(nd.op.target, Clbit):
block_cargs.add(nd.op.target)
elif isinstance(nd.op.target, ClassicalRegister):
block_cargs.update(nd.op.target)
else:
block_cargs.update(node_resources(nd.op.target).clbits)
block_qargs = [bit for bit in block_qargs if bit in wire_pos_map]
block_qargs.sort(key=wire_pos_map.get)
block_cargs = [bit for bit in block_cargs if bit in wire_pos_map]
block_cargs.sort(key=wire_pos_map.get)
new_node = DAGOpNode(op, block_qargs, block_cargs, dag=self)
try:
new_node._node_id = self._multi_graph.contract_nodes(
block_ids, new_node, check_cycle=cycle_check
)
except rx.DAGWouldCycle as ex:
raise DAGCircuitError(
"Replacing the specified node block would introduce a cycle"
) from ex
self._increment_op(op)
for nd in node_block:
self._decrement_op(nd.op)
return new_node
[docs] def substitute_node_with_dag(self, node, input_dag, wires=None, propagate_condition=True):
"""Replace one node with dag.
Args:
node (DAGOpNode): node to substitute
input_dag (DAGCircuit): circuit that will substitute the node
wires (list[Bit] | Dict[Bit, Bit]): gives an order for (qu)bits
in the input circuit. If a list, then the bits refer to those in the ``input_dag``,
and the order gets matched to the node wires by qargs first, then cargs, then
conditions. If a dictionary, then a mapping of bits in the ``input_dag`` to those
that the ``node`` acts on.
propagate_condition (bool): If ``True`` (default), then any ``condition`` attribute on
the operation within ``node`` is propagated to each node in the ``input_dag``. If
``False``, then the ``input_dag`` is assumed to faithfully implement suitable
conditional logic already. This is ignored for :class:`.ControlFlowOp`\\ s (i.e.
treated as if it is ``False``); replacements of those must already fulfil the same
conditional logic or this function would be close to useless for them.
Returns:
dict: maps node IDs from `input_dag` to their new node incarnations in `self`.
Raises:
DAGCircuitError: if met with unexpected predecessor/successors
"""
if not isinstance(node, DAGOpNode):
raise DAGCircuitError(f"expected node DAGOpNode, got {type(node)}")
if isinstance(wires, dict):
wire_map = wires
else:
wires = input_dag.wires if wires is None else wires
node_cargs = set(node.cargs)
node_wire_order = list(node.qargs) + list(node.cargs)
# If we're not propagating it, the number of wires in the input DAG should include the
# condition as well.
if not propagate_condition and self._operation_may_have_bits(node.op):
node_wire_order += [
bit for bit in self._bits_in_operation(node.op) if bit not in node_cargs
]
if len(wires) != len(node_wire_order):
raise DAGCircuitError(
f"bit mapping invalid: expected {len(node_wire_order)}, got {len(wires)}"
)
wire_map = dict(zip(wires, node_wire_order))
if len(wire_map) != len(node_wire_order):
raise DAGCircuitError("bit mapping invalid: some bits have duplicate entries")
for input_dag_wire, our_wire in wire_map.items():
if our_wire not in self.input_map:
raise DAGCircuitError(f"bit mapping invalid: {our_wire} is not in this DAG")
# Support mapping indiscriminately between Qubit and AncillaQubit, etc.
check_type = Qubit if isinstance(our_wire, Qubit) else Clbit
if not isinstance(input_dag_wire, check_type):
raise DAGCircuitError(
f"bit mapping invalid: {input_dag_wire} and {our_wire} are different bit types"
)
reverse_wire_map = {b: a for a, b in wire_map.items()}
# It doesn't make sense to try and propagate a condition from a control-flow op; a
# replacement for the control-flow op should implement the operation completely.
if (
propagate_condition
and not isinstance(node.op, ControlFlowOp)
and (op_condition := getattr(node.op, "condition", None)) is not None
):
in_dag = input_dag.copy_empty_like()
# The remapping of `condition` below is still using the old code that assumes a 2-tuple.
# This is because this remapping code only makes sense in the case of non-control-flow
# operations being replaced. These can only have the 2-tuple conditions, and the
# ability to set a condition at an individual node level will be deprecated and removed
# in favour of the new-style conditional blocks. The extra logic in here to add
# additional wires into the map as necessary would hugely complicate matters if we tried
# to abstract it out into the `VariableMapper` used elsewhere.
target, value = op_condition
if isinstance(target, Clbit):
new_target = reverse_wire_map.get(target, Clbit())
if new_target not in wire_map:
in_dag.add_clbits([new_target])
wire_map[new_target], reverse_wire_map[target] = target, new_target
target_cargs = {new_target}
else: # ClassicalRegister
mapped_bits = [reverse_wire_map.get(bit, Clbit()) for bit in target]
for ours, theirs in zip(target, mapped_bits):
# Update to any new dummy bits we just created to the wire maps.
wire_map[theirs], reverse_wire_map[ours] = ours, theirs
new_target = ClassicalRegister(bits=mapped_bits)
in_dag.add_creg(new_target)
target_cargs = set(new_target)
new_condition = (new_target, value)
for in_node in input_dag.topological_op_nodes():
if getattr(in_node.op, "condition", None) is not None:
raise DAGCircuitError(
"cannot propagate a condition to an element that already has one"
)
if target_cargs.intersection(in_node.cargs):
# This is for backwards compatibility with early versions of the method, as it is
# a tested part of the API. In the newer model of a condition being an integral
# part of the operation (not a separate property to be copied over), this error
# is overzealous, because it forbids a custom instruction from implementing the
# condition within its definition rather than at the top level.
raise DAGCircuitError(
"cannot propagate a condition to an element that acts on those bits"
)
new_op = copy.copy(in_node.op)
if new_condition:
if not isinstance(new_op, ControlFlowOp):
new_op = new_op.c_if(*new_condition)
else:
new_op.condition = new_condition
in_dag.apply_operation_back(new_op, in_node.qargs, in_node.cargs, check=False)
else:
in_dag = input_dag
if in_dag.global_phase:
self.global_phase += in_dag.global_phase
# Add wire from pred to succ if no ops on mapped wire on ``in_dag``
# rustworkx's substitute_node_with_subgraph lacks the DAGCircuit
# context to know what to do in this case (the method won't even see
# these nodes because they're filtered) so we manually retain the
# edges prior to calling substitute_node_with_subgraph and set the
# edge_map_fn callback kwarg to skip these edges when they're
# encountered.
for in_dag_wire, self_wire in wire_map.items():
input_node = in_dag.input_map[in_dag_wire]
output_node = in_dag.output_map[in_dag_wire]
if in_dag._multi_graph.has_edge(input_node._node_id, output_node._node_id):
pred = self._multi_graph.find_predecessors_by_edge(
node._node_id, lambda edge, wire=self_wire: edge == wire
)[0]
succ = self._multi_graph.find_successors_by_edge(
node._node_id, lambda edge, wire=self_wire: edge == wire
)[0]
self._multi_graph.add_edge(pred._node_id, succ._node_id, self_wire)
# Exlude any nodes from in_dag that are not a DAGOpNode or are on
# bits outside the set specified by the wires kwarg
def filter_fn(node):
if not isinstance(node, DAGOpNode):
return False
for qarg in node.qargs:
if qarg not in wire_map:
return False
return True
# Map edges into and out of node to the appropriate node from in_dag
def edge_map_fn(source, _target, self_wire):
wire = reverse_wire_map[self_wire]
# successor edge
if source == node._node_id:
wire_output_id = in_dag.output_map[wire]._node_id
out_index = in_dag._multi_graph.predecessor_indices(wire_output_id)[0]
# Edge directly from from input nodes to output nodes in in_dag are
# already handled prior to calling rustworkx. Don't map these edges
# in rustworkx.
if not isinstance(in_dag._multi_graph[out_index], DAGOpNode):
return None
# predecessor edge
else:
wire_input_id = in_dag.input_map[wire]._node_id
out_index = in_dag._multi_graph.successor_indices(wire_input_id)[0]
# Edge directly from from input nodes to output nodes in in_dag are
# already handled prior to calling rustworkx. Don't map these edges
# in rustworkx.
if not isinstance(in_dag._multi_graph[out_index], DAGOpNode):
return None
return out_index
# Adjust edge weights from in_dag
def edge_weight_map(wire):
return wire_map[wire]
node_map = self._multi_graph.substitute_node_with_subgraph(
node._node_id, in_dag._multi_graph, edge_map_fn, filter_fn, edge_weight_map
)
self._decrement_op(node.op)
variable_mapper = _classical_resource_map.VariableMapper(
self.cregs.values(), wire_map, self.add_creg
)
# Iterate over nodes of input_circuit and update wires in node objects migrated
# from in_dag
for old_node_index, new_node_index in node_map.items():
# update node attributes
old_node = in_dag._multi_graph[old_node_index]
if isinstance(old_node.op, SwitchCaseOp):
m_op = SwitchCaseOp(
variable_mapper.map_target(old_node.op.target),
old_node.op.cases_specifier(),
label=old_node.op.label,
)
elif getattr(old_node.op, "condition", None) is not None:
m_op = old_node.op
if not isinstance(old_node.op, ControlFlowOp):
new_condition = variable_mapper.map_condition(m_op.condition)
if new_condition is not None:
m_op = m_op.c_if(*new_condition)
else:
m_op.condition = variable_mapper.map_condition(m_op.condition)
else:
m_op = old_node.op
m_qargs = [wire_map[x] for x in old_node.qargs]
m_cargs = [wire_map[x] for x in old_node.cargs]
new_node = DAGOpNode(m_op, qargs=m_qargs, cargs=m_cargs, dag=self)
new_node._node_id = new_node_index
self._multi_graph[new_node_index] = new_node
self._increment_op(new_node.op)
return {k: self._multi_graph[v] for k, v in node_map.items()}
[docs] def substitute_node(self, node, op, inplace=False, propagate_condition=True):
"""Replace an DAGOpNode with a single operation. qargs, cargs and
conditions for the new operation will be inferred from the node to be
replaced. The new operation will be checked to match the shape of the
replaced operation.
Args:
node (DAGOpNode): Node to be replaced
op (qiskit.circuit.Operation): The :class:`qiskit.circuit.Operation`
instance to be added to the DAG
inplace (bool): Optional, default False. If True, existing DAG node
will be modified to include op. Otherwise, a new DAG node will
be used.
propagate_condition (bool): Optional, default True. If True, a condition on the
``node`` to be replaced will be applied to the new ``op``. This is the legacy
behaviour. If either node is a control-flow operation, this will be ignored. If
the ``op`` already has a condition, :exc:`.DAGCircuitError` is raised.
Returns:
DAGOpNode: the new node containing the added operation.
Raises:
DAGCircuitError: If replacement operation was incompatible with
location of target node.
"""
if not isinstance(node, DAGOpNode):
raise DAGCircuitError("Only DAGOpNodes can be replaced.")
if node.op.num_qubits != op.num_qubits or node.op.num_clbits != op.num_clbits:
raise DAGCircuitError(
"Cannot replace node of width ({} qubits, {} clbits) with "
"operation of mismatched width ({} qubits, {} clbits).".format(
node.op.num_qubits, node.op.num_clbits, op.num_qubits, op.num_clbits
)
)
# This might include wires that are inherent to the node, like in its `condition` or
# `target` fields, so might be wider than `node.op.num_{qu,cl}bits`.
current_wires = {wire for _, _, wire in self.edges(node)}
new_wires = set(node.qargs) | set(node.cargs)
if (new_condition := getattr(op, "condition", None)) is not None:
new_wires.update(condition_resources(new_condition).clbits)
elif isinstance(op, SwitchCaseOp):
if isinstance(op.target, Clbit):
new_wires.add(op.target)
elif isinstance(op.target, ClassicalRegister):
new_wires.update(op.target)
else:
new_wires.update(node_resources(op.target).clbits)
if propagate_condition and not (
isinstance(node.op, ControlFlowOp) or isinstance(op, ControlFlowOp)
):
if new_condition is not None:
raise DAGCircuitError(
"Cannot propagate a condition to an operation that already has one."
)
if (old_condition := getattr(node.op, "condition", None)) is not None:
if not isinstance(op, Instruction):
raise DAGCircuitError("Cannot add a condition on a generic Operation.")
if not isinstance(node.op, ControlFlowOp):
op = op.c_if(*old_condition)
else:
op.condition = old_condition
new_wires.update(condition_resources(old_condition).clbits)
if new_wires != current_wires:
# The new wires must be a non-strict subset of the current wires; if they add new wires,
# we'd not know where to cut the existing wire to insert the new dependency.
raise DAGCircuitError(
f"New operation '{op}' does not span the same wires as the old node '{node}'."
f" New wires: {new_wires}, old wires: {current_wires}."
)
if inplace:
if op.name != node.op.name:
self._increment_op(op)
self._decrement_op(node.op)
node.op = op
return node
new_node = copy.copy(node)
new_node.op = op
self._multi_graph[node._node_id] = new_node
if op.name != node.op.name:
self._increment_op(op)
self._decrement_op(node.op)
return new_node
[docs] def separable_circuits(self, remove_idle_qubits=False) -> List["DAGCircuit"]:
"""Decompose the circuit into sets of qubits with no gates connecting them.
Args:
remove_idle_qubits (bool): Flag denoting whether to remove idle qubits from
the separated circuits. If ``False``, each output circuit will contain the
same number of qubits as ``self``.
Returns:
List[DAGCircuit]: The circuits resulting from separating ``self`` into sets
of disconnected qubits
Each :class:`~.DAGCircuit` instance returned by this method will contain the same number of
clbits as ``self``. The global phase information in ``self`` will not be maintained
in the subcircuits returned by this method.
"""
connected_components = rx.weakly_connected_components(self._multi_graph)
# Collect each disconnected subgraph
disconnected_subgraphs = []
for components in connected_components:
disconnected_subgraphs.append(self._multi_graph.subgraph(list(components)))
# Helper function for ensuring rustworkx nodes are returned in lexicographical,
# topological order
def _key(x):
return x.sort_key
# Create new DAGCircuit objects from each of the rustworkx subgraph objects
decomposed_dags = []
for subgraph in disconnected_subgraphs:
new_dag = self.copy_empty_like()
new_dag.global_phase = 0
subgraph_is_classical = True
for node in rx.lexicographical_topological_sort(subgraph, key=_key):
if isinstance(node, DAGInNode):
if isinstance(node.wire, Qubit):
subgraph_is_classical = False
if not isinstance(node, DAGOpNode):
continue
new_dag.apply_operation_back(node.op, node.qargs, node.cargs, check=False)
# Ignore DAGs created for empty clbits
if not subgraph_is_classical:
decomposed_dags.append(new_dag)
if remove_idle_qubits:
for dag in decomposed_dags:
dag.remove_qubits(*(bit for bit in dag.idle_wires() if isinstance(bit, Qubit)))
return decomposed_dags
[docs] def swap_nodes(self, node1, node2):
"""Swap connected nodes e.g. due to commutation.
Args:
node1 (OpNode): predecessor node
node2 (OpNode): successor node
Raises:
DAGCircuitError: if either node is not an OpNode or nodes are not connected
"""
if not (isinstance(node1, DAGOpNode) and isinstance(node2, DAGOpNode)):
raise DAGCircuitError("nodes to swap are not both DAGOpNodes")
try:
connected_edges = self._multi_graph.get_all_edge_data(node1._node_id, node2._node_id)
except rx.NoEdgeBetweenNodes as no_common_edge:
raise DAGCircuitError("attempt to swap unconnected nodes") from no_common_edge
node1_id = node1._node_id
node2_id = node2._node_id
for edge in connected_edges[::-1]:
edge_find = lambda x, y=edge: x == y
edge_parent = self._multi_graph.find_predecessors_by_edge(node1_id, edge_find)[0]
self._multi_graph.remove_edge(edge_parent._node_id, node1_id)
self._multi_graph.add_edge(edge_parent._node_id, node2_id, edge)
edge_child = self._multi_graph.find_successors_by_edge(node2_id, edge_find)[0]
self._multi_graph.remove_edge(node1_id, node2_id)
self._multi_graph.add_edge(node2_id, node1_id, edge)
self._multi_graph.remove_edge(node2_id, edge_child._node_id)
self._multi_graph.add_edge(node1_id, edge_child._node_id, edge)
[docs] def node(self, node_id):
"""Get the node in the dag.
Args:
node_id(int): Node identifier.
Returns:
node: the node.
"""
return self._multi_graph[node_id]
[docs] def nodes(self):
"""Iterator for node values.
Yield:
node: the node.
"""
yield from self._multi_graph.nodes()
[docs] def edges(self, nodes=None):
"""Iterator for edge values and source and dest node
This works by returning the output edges from the specified nodes. If
no nodes are specified all edges from the graph are returned.
Args:
nodes(DAGOpNode, DAGInNode, or DAGOutNode|list(DAGOpNode, DAGInNode, or DAGOutNode):
Either a list of nodes or a single input node. If none is specified,
all edges are returned from the graph.
Yield:
edge: the edge in the same format as out_edges the tuple
(source node, destination node, edge data)
"""
if nodes is None:
nodes = self._multi_graph.nodes()
elif isinstance(nodes, (DAGOpNode, DAGInNode, DAGOutNode)):
nodes = [nodes]
for node in nodes:
raw_nodes = self._multi_graph.out_edges(node._node_id)
for source, dest, edge in raw_nodes:
yield (self._multi_graph[source], self._multi_graph[dest], edge)
[docs] def op_nodes(self, op=None, include_directives=True):
"""Get the list of "op" nodes in the dag.
Args:
op (Type): :class:`qiskit.circuit.Operation` subclass op nodes to
return. If None, return all op nodes.
include_directives (bool): include `barrier`, `snapshot` etc.
Returns:
list[DAGOpNode]: the list of node ids containing the given op.
"""
nodes = []
for node in self._multi_graph.nodes():
if isinstance(node, DAGOpNode):
if not include_directives and getattr(node.op, "_directive", False):
continue
if op is None or isinstance(node.op, op):
nodes.append(node)
return nodes
[docs] def gate_nodes(self):
"""Get the list of gate nodes in the dag.
Returns:
list[DAGOpNode]: the list of DAGOpNodes that represent gates.
"""
nodes = []
for node in self.op_nodes():
if isinstance(node.op, Gate):
nodes.append(node)
return nodes
[docs] def named_nodes(self, *names):
"""Get the set of "op" nodes with the given name."""
named_nodes = []
for node in self._multi_graph.nodes():
if isinstance(node, DAGOpNode) and node.op.name in names:
named_nodes.append(node)
return named_nodes
[docs] def two_qubit_ops(self):
"""Get list of 2 qubit operations. Ignore directives like snapshot and barrier."""
ops = []
for node in self.op_nodes(include_directives=False):
if len(node.qargs) == 2:
ops.append(node)
return ops
[docs] def multi_qubit_ops(self):
"""Get list of 3+ qubit operations. Ignore directives like snapshot and barrier."""
ops = []
for node in self.op_nodes(include_directives=False):
if len(node.qargs) >= 3:
ops.append(node)
return ops
[docs] def longest_path(self):
"""Returns the longest path in the dag as a list of DAGOpNodes, DAGInNodes, and DAGOutNodes."""
return [self._multi_graph[x] for x in rx.dag_longest_path(self._multi_graph)]
[docs] def successors(self, node):
"""Returns iterator of the successors of a node as DAGOpNodes and DAGOutNodes."""
return iter(self._multi_graph.successors(node._node_id))
[docs] def predecessors(self, node):
"""Returns iterator of the predecessors of a node as DAGOpNodes and DAGInNodes."""
return iter(self._multi_graph.predecessors(node._node_id))
[docs] def is_successor(self, node, node_succ):
"""Checks if a second node is in the successors of node."""
return self._multi_graph.has_edge(node._node_id, node_succ._node_id)
[docs] def is_predecessor(self, node, node_pred):
"""Checks if a second node is in the predecessors of node."""
return self._multi_graph.has_edge(node_pred._node_id, node._node_id)
[docs] def quantum_predecessors(self, node):
"""Returns iterator of the predecessors of a node that are
connected by a quantum edge as DAGOpNodes and DAGInNodes."""
return iter(
self._multi_graph.find_predecessors_by_edge(
node._node_id, lambda edge_data: isinstance(edge_data, Qubit)
)
)
[docs] def classical_predecessors(self, node):
"""Returns iterator of the predecessors of a node that are
connected by a classical edge as DAGOpNodes and DAGInNodes."""
return iter(
self._multi_graph.find_predecessors_by_edge(
node._node_id, lambda edge_data: isinstance(edge_data, Clbit)
)
)
[docs] def ancestors(self, node):
"""Returns set of the ancestors of a node as DAGOpNodes and DAGInNodes."""
return {self._multi_graph[x] for x in rx.ancestors(self._multi_graph, node._node_id)}
[docs] def descendants(self, node):
"""Returns set of the descendants of a node as DAGOpNodes and DAGOutNodes."""
return {self._multi_graph[x] for x in rx.descendants(self._multi_graph, node._node_id)}
[docs] def bfs_successors(self, node):
"""
Returns an iterator of tuples of (DAGNode, [DAGNodes]) where the DAGNode is the current node
and [DAGNode] is its successors in BFS order.
"""
return iter(rx.bfs_successors(self._multi_graph, node._node_id))
[docs] def quantum_successors(self, node):
"""Returns iterator of the successors of a node that are
connected by a quantum edge as Opnodes and DAGOutNodes."""
return iter(
self._multi_graph.find_successors_by_edge(
node._node_id, lambda edge_data: isinstance(edge_data, Qubit)
)
)
[docs] def classical_successors(self, node):
"""Returns iterator of the successors of a node that are
connected by a classical edge as DAGOpNodes and DAGInNodes."""
return iter(
self._multi_graph.find_successors_by_edge(
node._node_id, lambda edge_data: isinstance(edge_data, Clbit)
)
)
[docs] def remove_op_node(self, node):
"""Remove an operation node n.
Add edges from predecessors to successors.
"""
if not isinstance(node, DAGOpNode):
raise DAGCircuitError(
'The method remove_op_node only works on DAGOpNodes. A "%s" '
"node type was wrongly provided." % type(node)
)
self._multi_graph.remove_node_retain_edges(
node._node_id, use_outgoing=False, condition=lambda edge1, edge2: edge1 == edge2
)
self._decrement_op(node.op)
[docs] def remove_ancestors_of(self, node):
"""Remove all of the ancestor operation nodes of node."""
anc = rx.ancestors(self._multi_graph, node)
# TODO: probably better to do all at once using
# multi_graph.remove_nodes_from; same for related functions ...
for anc_node in anc:
if isinstance(anc_node, DAGOpNode):
self.remove_op_node(anc_node)
[docs] def remove_descendants_of(self, node):
"""Remove all of the descendant operation nodes of node."""
desc = rx.descendants(self._multi_graph, node)
for desc_node in desc:
if isinstance(desc_node, DAGOpNode):
self.remove_op_node(desc_node)
[docs] def remove_nonancestors_of(self, node):
"""Remove all of the non-ancestors operation nodes of node."""
anc = rx.ancestors(self._multi_graph, node)
comp = list(set(self._multi_graph.nodes()) - set(anc))
for n in comp:
if isinstance(n, DAGOpNode):
self.remove_op_node(n)
[docs] def remove_nondescendants_of(self, node):
"""Remove all of the non-descendants operation nodes of node."""
dec = rx.descendants(self._multi_graph, node)
comp = list(set(self._multi_graph.nodes()) - set(dec))
for n in comp:
if isinstance(n, DAGOpNode):
self.remove_op_node(n)
[docs] def front_layer(self):
"""Return a list of op nodes in the first layer of this dag."""
graph_layers = self.multigraph_layers()
try:
next(graph_layers) # Remove input nodes
except StopIteration:
return []
op_nodes = [node for node in next(graph_layers) if isinstance(node, DAGOpNode)]
return op_nodes
[docs] def layers(self):
"""Yield a shallow view on a layer of this DAGCircuit for all d layers of this circuit.
A layer is a circuit whose gates act on disjoint qubits, i.e.,
a layer has depth 1. The total number of layers equals the
circuit depth d. The layers are indexed from 0 to d-1 with the
earliest layer at index 0. The layers are constructed using a
greedy algorithm. Each returned layer is a dict containing
{"graph": circuit graph, "partition": list of qubit lists}.
The returned layer contains new (but semantically equivalent) DAGOpNodes, DAGInNodes,
and DAGOutNodes. These are not the same as nodes of the original dag, but are equivalent
via DAGNode.semantic_eq(node1, node2).
TODO: Gates that use the same cbits will end up in different
layers as this is currently implemented. This may not be
the desired behavior.
"""
graph_layers = self.multigraph_layers()
try:
next(graph_layers) # Remove input nodes
except StopIteration:
return
for graph_layer in graph_layers:
# Get the op nodes from the layer, removing any input and output nodes.
op_nodes = [node for node in graph_layer if isinstance(node, DAGOpNode)]
# Sort to make sure they are in the order they were added to the original DAG
# It has to be done by node_id as graph_layer is just a list of nodes
# with no implied topology
# Drawing tools rely on _node_id to infer order of node creation
# so we need this to be preserved by layers()
op_nodes.sort(key=lambda nd: nd._node_id)
# Stop yielding once there are no more op_nodes in a layer.
if not op_nodes:
return
# Construct a shallow copy of self
new_layer = self.copy_empty_like()
for node in op_nodes:
# this creates new DAGOpNodes in the new_layer
new_layer.apply_operation_back(node.op, node.qargs, node.cargs, check=False)
# The quantum registers that have an operation in this layer.
support_list = [
op_node.qargs
for op_node in new_layer.op_nodes()
if not getattr(op_node.op, "_directive", False)
]
yield {"graph": new_layer, "partition": support_list}
[docs] def serial_layers(self):
"""Yield a layer for all gates of this circuit.
A serial layer is a circuit with one gate. The layers have the
same structure as in layers().
"""
for next_node in self.topological_op_nodes():
new_layer = self.copy_empty_like()
# Save the support of the operation we add to the layer
support_list = []
# Operation data
op = copy.copy(next_node.op)
qargs = copy.copy(next_node.qargs)
cargs = copy.copy(next_node.cargs)
# Add node to new_layer
new_layer.apply_operation_back(op, qargs, cargs, check=False)
# Add operation to partition
if not getattr(next_node.op, "_directive", False):
support_list.append(list(qargs))
l_dict = {"graph": new_layer, "partition": support_list}
yield l_dict
[docs] def multigraph_layers(self):
"""Yield layers of the multigraph."""
first_layer = [x._node_id for x in self.input_map.values()]
return iter(rx.layers(self._multi_graph, first_layer))
[docs] def collect_runs(self, namelist):
"""Return a set of non-conditional runs of "op" nodes with the given names.
For example, "... h q[0]; cx q[0],q[1]; cx q[0],q[1]; h q[1]; .."
would produce the tuple of cx nodes as an element of the set returned
from a call to collect_runs(["cx"]). If instead the cx nodes were
"cx q[0],q[1]; cx q[1],q[0];", the method would still return the
pair in a tuple. The namelist can contain names that are not
in the circuit's basis.
Nodes must have only one successor to continue the run.
"""
def filter_fn(node):
return (
isinstance(node, DAGOpNode)
and node.op.name in namelist
and getattr(node.op, "condition", None) is None
)
group_list = rx.collect_runs(self._multi_graph, filter_fn)
return {tuple(x) for x in group_list}
[docs] def collect_1q_runs(self):
"""Return a set of non-conditional runs of 1q "op" nodes."""
def filter_fn(node):
return (
isinstance(node, DAGOpNode)
and len(node.qargs) == 1
and len(node.cargs) == 0
and getattr(node.op, "condition", None) is None
and not node.op.is_parameterized()
and isinstance(node.op, Gate)
and hasattr(node.op, "__array__")
)
return rx.collect_runs(self._multi_graph, filter_fn)
[docs] def collect_2q_runs(self):
"""Return a set of non-conditional runs of 2q "op" nodes."""
to_qid = {}
for i, qubit in enumerate(self.qubits):
to_qid[qubit] = i
def filter_fn(node):
if isinstance(node, DAGOpNode):
return (
isinstance(node.op, Gate)
and len(node.qargs) <= 2
and not getattr(node.op, "condition", None)
and not node.op.is_parameterized()
)
else:
return None
def color_fn(edge):
if isinstance(edge, Qubit):
return to_qid[edge]
else:
return None
return rx.collect_bicolor_runs(self._multi_graph, filter_fn, color_fn)
[docs] def nodes_on_wire(self, wire, only_ops=False):
"""
Iterator for nodes that affect a given wire.
Args:
wire (Bit): the wire to be looked at.
only_ops (bool): True if only the ops nodes are wanted;
otherwise, all nodes are returned.
Yield:
Iterator: the successive nodes on the given wire
Raises:
DAGCircuitError: if the given wire doesn't exist in the DAG
"""
current_node = self.input_map.get(wire, None)
if not current_node:
raise DAGCircuitError("The given wire %s is not present in the circuit" % str(wire))
more_nodes = True
while more_nodes:
more_nodes = False
# allow user to just get ops on the wire - not the input/output nodes
if isinstance(current_node, DAGOpNode) or not only_ops:
yield current_node
try:
current_node = self._multi_graph.find_adjacent_node_by_edge(
current_node._node_id, lambda x: wire == x
)
more_nodes = True
except rx.NoSuitableNeighbors:
pass
[docs] def count_ops(self, *, recurse: bool = True):
"""Count the occurrences of operation names.
Args:
recurse: if ``True`` (default), then recurse into control-flow operations. In all
cases, this counts only the number of times the operation appears in any possible
block; both branches of if-elses are counted, and for- and while-loop blocks are
only counted once.
Returns:
Mapping[str, int]: a mapping of operation names to the number of times it appears.
"""
if not recurse or not CONTROL_FLOW_OP_NAMES.intersection(self._op_names):
return self._op_names.copy()
# pylint: disable=cyclic-import
from qiskit.converters import circuit_to_dag
def inner(dag, counts):
for name, count in dag._op_names.items():
counts[name] += count
for node in dag.op_nodes(ControlFlowOp):
for block in node.op.blocks:
counts = inner(circuit_to_dag(block), counts)
return counts
return dict(inner(self, defaultdict(int)))
[docs] def count_ops_longest_path(self):
"""Count the occurrences of operation names on the longest path.
Returns a dictionary of counts keyed on the operation name.
"""
op_dict = {}
path = self.longest_path()
path = path[1:-1] # remove qubits at beginning and end of path
for node in path:
name = node.op.name
if name not in op_dict:
op_dict[name] = 1
else:
op_dict[name] += 1
return op_dict
[docs] def quantum_causal_cone(self, qubit):
"""
Returns causal cone of a qubit.
A qubit's causal cone is the set of qubits that can influence the output of that
qubit through interactions, whether through multi-qubit gates or operations. Knowing
the causal cone of a qubit can be useful when debugging faulty circuits, as it can
help identify which wire(s) may be causing the problem.
This method does not consider any classical data dependency in the ``DAGCircuit``,
classical bit wires are ignored for the purposes of building the causal cone.
Args:
qubit (Qubit): The output qubit for which we want to find the causal cone.
Returns:
Set[Qubit]: The set of qubits whose interactions affect ``qubit``.
"""
# Retrieve the output node from the qubit
output_node = self.output_map.get(qubit, None)
if not output_node:
raise DAGCircuitError(f"Qubit {qubit} is not part of this circuit.")
# Add the qubit to the causal cone.
qubits_to_check = {qubit}
# Add predecessors of output node to the queue.
queue = deque(self.predecessors(output_node))
# While queue isn't empty
while queue:
# Pop first element.
node_to_check = queue.popleft()
# Check whether element is input or output node.
if isinstance(node_to_check, DAGOpNode):
# Keep all the qubits in the operation inside a set.
qubit_set = set(node_to_check.qargs)
# Check if there are any qubits in common and that the operation is not a barrier.
if (
len(qubit_set.intersection(qubits_to_check)) > 0
and node_to_check.op.name != "barrier"
and not getattr(node_to_check.op, "_directive")
):
# If so, add all the qubits to the causal cone.
qubits_to_check = qubits_to_check.union(qubit_set)
# For each predecessor of the current node, filter input/output nodes,
# also make sure it has at least one qubit in common. Then append.
for node in self.quantum_predecessors(node_to_check):
if (
isinstance(node, DAGOpNode)
and len(qubits_to_check.intersection(set(node.qargs))) > 0
):
queue.append(node)
return qubits_to_check
[docs] def properties(self):
"""Return a dictionary of circuit properties."""
summary = {
"size": self.size(),
"depth": self.depth(),
"width": self.width(),
"qubits": self.num_qubits(),
"bits": self.num_clbits(),
"factors": self.num_tensor_factors(),
"operations": self.count_ops(),
}
return summary
[docs] def draw(self, scale=0.7, filename=None, style="color"):
"""
Draws the dag circuit.
This function needs `pydot <https://github.com/erocarrera/pydot>`_, which in turn needs
`Graphviz <https://www.graphviz.org/>`_ to be installed.
Args:
scale (float): scaling factor
filename (str): file path to save image to (format inferred from name)
style (str):
'plain': B&W graph;
'color' (default): color input/output/op nodes
Returns:
Ipython.display.Image: if in Jupyter notebook and not saving to file,
otherwise None.
"""
from qiskit.visualization.dag_visualization import dag_drawer
return dag_drawer(dag=self, scale=scale, filename=filename, style=style)
def _warn_none_args():
warnings.warn(
"Passing 'None' as the qubits or clbits of an operation to 'DAGCircuit' methods"
" is deprecated since Qiskit 0.45 and will be removed in Qiskit 1.0. Instead, pass '()'.",
DeprecationWarning,
stacklevel=3,
)