DAGCircuit

DAGCircuit.add_calibration(gate, qubits, schedule, params=None)

Register a low-level, custom pulse definition for the given gate.

Parameters

• 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.

DAGCircuit.add_clbits(clbits)

Add individual clbit wires.

DAGCircuit.add_creg(creg)

Add all wires in a classical register.

DAGCircuit.add_qreg(qreg)

Add all wires in a quantum register.

DAGCircuit.add_qubits(qubits)

Add individual qubit wires.

DAGCircuit.ancestors(node)

Returns set of the ancestors of a node as DAGOpNodes and DAGInNodes.

DAGCircuit.apply_operation_back(op, qargs=(), cargs=())

Apply an operation to the output of the circuit.

Parameters

• 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

Returns

the node for the op that was added to the dag

Return type

DAGOpNode

Raises

DAGCircuitError – if a leaf node is connected to multiple outputs

DAGCircuit.apply_operation_front(op, qargs=(), cargs=())

Apply an operation to the input of the circuit.

Parameters

• 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

Returns

the node for the op that was added to the dag

Return type

DAGOpNode

Raises

DAGCircuitError – if initial nodes connected to multiple out edges

DAGCircuit.bfs_successors(node)

Returns an iterator of tuples of (DAGNode, [DAGNodes]) where the DAGNode is the current node and [DAGNode] is its successors in BFS order.

DAGCircuit.collect_1q_runs()

Return a set of non-conditional runs of 1q “op” nodes.

DAGCircuit.collect_2q_runs()

Return a set of non-conditional runs of 2q “op” nodes.

DAGCircuit.collect_runs(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.

DAGCircuit.compose(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.

Parameters

• 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

the composed dag (returns None if inplace==True).

Return type

DAGCircuit

Raises

DAGCircuitError – if other is wider or there are duplicate edge mappings.

DAGCircuit.copy_empty_like()

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

An empty copy of self.

Return type

DAGCircuit

DAGCircuit.count_ops(*, recurse=True)

Count the occurrences of operation names.

Parameters

recurse (bool) – 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

a mapping of operation names to the number of times it appears.

Return type

Mapping[str, int]

DAGCircuit.count_ops_longest_path()

Count the occurrences of operation names on the longest path.

Returns a dictionary of counts keyed on the operation name.

DAGCircuit.depth(*, recurse=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 staticly known.

Parameters

recurse (bool) – 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 DAGCircuitError if any control flow is present, to avoid silently returning a nonsensical number.

Returns

the circuit depth

Return type

int

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.

DAGCircuit.descendants(node)

Returns set of the descendants of a node as DAGOpNodes and DAGOutNodes.

DAGCircuit.draw(scale=0.7, filename=None, style='color')

Draws the dag circuit.

This function needs pydot, which in turn needs Graphviz to be installed.

Parameters

• 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

if in Jupyter notebook and not saving to file, otherwise None.

Return type

Ipython.display.Image

DAGCircuit.edges(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.

Parameters

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.

Yields

edge –

the edge in the same format as out_edges the tuple

(source node, destination node, edge data)

DAGCircuit.front_layer()

Return a list of op nodes in the first layer of this dag.

DAGCircuit.gate_nodes()

Get the list of gate nodes in the dag.

Returns

the list of DAGOpNodes that represent gates.

Return type

list[DAGOpNode]

DAGCircuit.has_calibration_for(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.

DAGCircuit.idle_wires(ignore=None)

Return idle wires.

Parameters

ignore (list(str)) – List of node names to ignore. Default: []

Yields

Bit – Bit in idle wire.

Raises

DAGCircuitError – If the DAG is invalid

DAGCircuit.is_predecessor(node, node_pred)

Checks if a second node is in the predecessors of node.

DAGCircuit.is_successor(node, node_succ)

Checks if a second node is in the successors of node.

DAGCircuit.layers()

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.

DAGCircuit.longest_path()

Returns the longest path in the dag as a list of DAGOpNodes, DAGInNodes, and DAGOutNodes.

DAGCircuit.multi_qubit_ops()

Get list of 3+ qubit operations. Ignore directives like snapshot and barrier.

DAGCircuit.multigraph_layers()

Yield layers of the multigraph.

DAGCircuit.named_nodes(*names)

Get the set of “op” nodes with the given name.

DAGCircuit.node(node_id)

Get the node in the dag.

Parameters

node_id (int) – Node identifier.

Returns

the node.

Return type

node

DAGCircuit.nodes()

Iterator for node values.

Yields

node – the node.

DAGCircuit.nodes_on_wire(wire, only_ops=False)

Iterator for nodes that affect a given wire.

Parameters

• wire (Bit) – the wire to be looked at.
• only_ops (bool) – True if only the ops nodes are wanted; otherwise, all nodes are returned.

Yields

Iterator – the successive nodes on the given wire

Raises

DAGCircuitError – if the given wire doesn’t exist in the DAG

DAGCircuit.num_clbits()

Return the total number of classical bits used by the circuit.

DAGCircuit.num_qubits()

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].

DAGCircuit.num_tensor_factors()

Compute how many components the circuit can decompose into.

DAGCircuit.op_nodes(op=None, include_directives=True)

Get the list of “op” nodes in the dag.

Parameters

• op (Type) – qiskit.circuit.Operation subclass op nodes to return. If None, return all op nodes.
• include_directives (bool) – include barrier, snapshot etc.

Returns

the list of node ids containing the given op.

Return type

list[DAGOpNode]

DAGCircuit.predecessors(node)

Returns iterator of the predecessors of a node as DAGOpNodes and DAGInNodes.

DAGCircuit.properties()

Return a dictionary of circuit properties.

DAGCircuit.quantum_predecessors(node)

Returns iterator of the predecessors of a node that are connected by a quantum edge as DAGOpNodes and DAGInNodes.

DAGCircuit.quantum_successors(node)

Returns iterator of the successors of a node that are connected by a quantum edge as Opnodes and DAGOutNodes.

DAGCircuit.remove_all_ops_named(opname)

Remove all operation nodes with the given name.

DAGCircuit.remove_ancestors_of(node)

Remove all of the ancestor operation nodes of node.

DAGCircuit.remove_clbits(*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.

Parameters

clbits (List[Clbit]) – The bits to remove.

Raises

DAGCircuitError – a clbit is not a Clbit, is not in the circuit, or is not idle.

DAGCircuit.remove_cregs(*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. –

DAGCircuit.remove_descendants_of(node)

Remove all of the descendant operation nodes of node.

DAGCircuit.remove_nonancestors_of(node)

Remove all of the non-ancestors operation nodes of node.

DAGCircuit.remove_nondescendants_of(node)

Remove all of the non-descendants operation nodes of node.

DAGCircuit.remove_op_node(node)

Remove an operation node n.

Add edges from predecessors to successors.

DAGCircuit.remove_qregs(*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. –

DAGCircuit.remove_qubits(*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.

Parameters

qubits (List[Qubit]) – The bits to remove.

Raises

DAGCircuitError – a qubit is not a Qubit, is not in the circuit, or is not idle.

DAGCircuit.replace_block_with_op(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.

Parameters

• 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[Qubit, int]) – The dictionary mapping the qarg to the position. This is necessary to reconstruct the qarg order over multiple gates in the combined single op node.
• 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

The op node that replaces the block.

Return type

DAGOpNode

DAGCircuit.reverse_ops()

Reverse the operations in the self circuit.

Returns

the reversed dag.

Return type

DAGCircuit

DAGCircuit.serial_layers()

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().

DAGCircuit.size(*, recurse=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.

Parameters

recurse (bool) – 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 DAGCircuitError if any control flow is present, to avoid silently returning a mostly meaningless number.

Returns

the circuit size

Return type

int

Raises

DAGCircuitError – if an unknown ControlFlowOp is present in a call with recurse=True, or any control flow is present in a non-recursive call.

DAGCircuit.substitute_node(node, op, inplace=False)

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.

Parameters

• node (DAGOpNode) – Node to be replaced
• op (qiskit.circuit.Operation) – The 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.

Returns

the new node containing the added operation.

Return type

DAGOpNode

Raises

• DAGCircuitError – If replacement operation was incompatible with
• location of target node. –

DAGCircuit.substitute_node_with_dag(node, input_dag, wires=None, propagate_condition=True)

Replace one node with dag.

Parameters

• 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.

Returns

maps node IDs from input_dag to their new node incarnations in self.

Return type

dict

Raises

DAGCircuitError – if met with unexpected predecessor/successors

DAGCircuit.successors(node)

Returns iterator of the successors of a node as DAGOpNodes and DAGOutNodes.

DAGCircuit.topological_nodes(key=None)

Yield nodes in topological order.

Parameters

key (Callable) – A callable which will take a DAGNode object and return a string sort key. If not specified the sort_key attribute will be used as the sort key for each node.

Returns

node in topological order

Return type

generator(DAGOpNode, DAGInNode, or DAGOutNode)

DAGCircuit.topological_op_nodes(key=None)

Yield op nodes in topological order.

Allowed to pass in specific key to break ties in top order

Parameters

key (Callable) – A callable which will take a DAGNode object and return a string sort key. If not specified the sort_key attribute will be used as the sort key for each node.

Returns

op node in topological order

Return type

generator(DAGOpNode)

DAGCircuit.two_qubit_ops()

Get list of 2 qubit operations. Ignore directives like snapshot and barrier.

DAGCircuit.width()

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 calibration dictionary.

The custom pulse definition of a given gate is of the form

{‘gate_name’: {(qubits, params): schedule}}

Return the global phase of the circuit.

Returns the number of nodes in the dag.

Return a list of the wires in order.