kahypar_cut(graph, num_fragments, imbalance=None, edge_weights=None, node_weights=None, fragment_weights=None, hyperwire_weight=1, seed=None, config_path=None, trial=None, verbose=False)[source]

Calls KaHyPar to partition a graph.


Requires KaHyPar to be installed separately. For Linux and Mac users, KaHyPar can be installed using pip install kahypar. Windows users can follow the instructions here to compile from source.

  • graph (nx.MultiDiGraph) – The graph to be partitioned.

  • num_fragments (int) – Desired number of fragments.

  • imbalance (int) – Imbalance factor of the partitioning. Defaults to KaHyPar’s determination.

  • edge_weights (List[Union[int, float]]) – Weights for edges. Defaults to unit-weighted edges.

  • node_weights (List[Union[int, float]]) – Weights for nodes. Defaults to unit-weighted nodes.

  • fragment_weights (List[Union[int, float]]) – Maximum size constraints by fragment. Defaults to no such constraints, with imbalance the only parameter affecting fragment sizes.

  • hyperwire_weight (int) – Weight on the artificially appended hyperedges representing wires. Setting it to 0 leads to no such insertion. If greater than 0, hyperedges will be appended with the provided weight, to encourage the resulting fragments to cluster gates on the same wire together. Defaults to 1.

  • seed (int) – KaHyPar’s seed. Defaults to the seed in the config file which defaults to -1, i.e. unfixed seed.

  • config_path (str) – KaHyPar’s .ini config file path. Defaults to its SEA20 paper config.

  • trial (int) – trial id for summary label creation. Defaults to None.

  • verbose (bool) – Flag for printing KaHyPar’s output summary. Defaults to False.


List of cut edges.

Return type

List[Union[int, Any]]


Consider the following 2-wire circuit with one CNOT gate connecting the wires:

with qml.tape.QuantumTape() as tape:
    qml.RX(0.432, wires=0)
    qml.RY(0.543, wires="a")
    qml.CNOT(wires=[0, "a"])
    qml.RZ(0.240, wires=0)
    qml.RZ(0.133, wires="a")
    qml.RX(0.432, wires=0)
    qml.RY(0.543, wires="a")

We can let KaHyPar automatically find the optimal edges to place cuts:

>>> graph = qml.transforms.qcut.tape_to_graph(tape)
>>> cut_edges = qml.transforms.qcut.kahypar_cut(
>>> cut_edges
[(CNOT(wires=[0, 'a']), RZ(0.24, wires=[0]), 0)]