Source code for qiskit.circuit.equivalence

# This code is part of Qiskit.
#
# (C) Copyright IBM 2020.
#
# 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.

"""Gate equivalence library."""

import io
from collections import namedtuple

import retworkx as rx

from qiskit.exceptions import MissingOptionalLibraryError
from .exceptions import CircuitError
from .parameterexpression import ParameterExpression


Key = namedtuple("Key", ["name", "num_qubits"])

Entry = namedtuple("Entry", ["search_base", "equivalences"])

Equivalence = namedtuple("Equivalence", ["params", "circuit"])  # Ordered to match Gate.params


class EquivalenceLibrary:
    """A library providing a one-way mapping of Gates to their equivalent
    implementations as QuantumCircuits."""

    def __init__(self, *, base=None):
        """Create a new equivalence library.

        Args:
            base (Optional[EquivalenceLibrary]):  Base equivalence library to
                will be referenced if an entry is not found in this library.
        """
        self._base = base

        self._map = {}

    def add_equivalence(self, gate, equivalent_circuit):
        """Add a new equivalence to the library. Future queries for the Gate
        will include the given circuit, in addition to all existing equivalences
        (including those from base).

        Parameterized Gates (those including `qiskit.circuit.Parameters` in their
        `Gate.params`) can be marked equivalent to parameterized circuits,
        provided the parameters match.

        Args:
            gate (Gate): A Gate instance.
            equivalent_circuit (QuantumCircuit): A circuit equivalently
                implementing the given Gate.
        """

        _raise_if_shape_mismatch(gate, equivalent_circuit)
        _raise_if_param_mismatch(gate.params, equivalent_circuit.parameters)

        key = Key(name=gate.name, num_qubits=gate.num_qubits)

        equiv = Equivalence(params=gate.params.copy(), circuit=equivalent_circuit.copy())

        if key not in self._map:
            self._map[key] = Entry(search_base=True, equivalences=[])

        self._map[key].equivalences.append(equiv)

    def has_entry(self, gate):
        """Check if a library contains any decompositions for gate.

        Args:
            gate (Gate): A Gate instance.

        Returns:
            Bool: True if gate has a known decomposition in the library.
                False otherwise.
        """

        key = Key(name=gate.name, num_qubits=gate.num_qubits)

        return key in self._map or (self._base.has_entry(gate) if self._base is not None else False)

    def set_entry(self, gate, entry):
        """Set the equivalence record for a Gate. Future queries for the Gate
        will return only the circuits provided.

        Parameterized Gates (those including `qiskit.circuit.Parameters` in their
        `Gate.params`) can be marked equivalent to parameterized circuits,
        provided the parameters match.

        Args:
            gate (Gate): A Gate instance.
            entry (List['QuantumCircuit']) : A list of QuantumCircuits, each
                equivalently implementing the given Gate.
        """

        for equiv in entry:
            _raise_if_shape_mismatch(gate, equiv)
            _raise_if_param_mismatch(gate.params, equiv.parameters)

        key = Key(name=gate.name, num_qubits=gate.num_qubits)

        equivs = [Equivalence(params=gate.params.copy(), circuit=equiv.copy()) for equiv in entry]

        self._map[key] = Entry(search_base=False, equivalences=equivs)

    def get_entry(self, gate):
        """Gets the set of QuantumCircuits circuits from the library which
        equivalently implement the given Gate.

        Parameterized circuits will have their parameters replaced with the
        corresponding entries from Gate.params.

        Args:
            gate (Gate) - Gate: A Gate instance.

        Returns:
            List[QuantumCircuit]: A list of equivalent QuantumCircuits. If empty,
                library contains no known decompositions of Gate.

                Returned circuits will be ordered according to their insertion in
                the library, from earliest to latest, from top to base. The
                ordering of the StandardEquivalenceLibrary will not generally be
                consistent across Qiskit versions.
        """

        key = Key(name=gate.name, num_qubits=gate.num_qubits)

        query_params = gate.params

        return [_rebind_equiv(equiv, query_params) for equiv in self._get_equivalences(key)]

    def draw(self, filename=None):
        """Draws the equivalence relations available in the library.

        Args:
            filename (str): An optional path to write the output image to
                if specified this method will return None.

        Returns:
            PIL.Image or IPython.display.SVG: Drawn equivalence library as an
                IPython SVG if in a jupyter notebook, or as a PIL.Image otherwise.

        Raises:
            MissingOptionalLibraryError: when pydot or pillow are not installed.
        """
        try:
            import pydot

            has_pydot = True
        except ImportError:
            has_pydot = False
        try:
            from PIL import Image

            has_pil = True
        except ImportError:
            has_pil = False

        if not has_pydot:
            raise MissingOptionalLibraryError(
                libname="pydot",
                name="EquivalenceLibrary.draw",
                pip_install="pip install pydot",
            )
        if not has_pil and not filename:
            raise MissingOptionalLibraryError(
                libname="pillow",
                name="EquivalenceLibrary.draw",
                pip_install="pip install pillow",
            )

        try:
            from IPython.display import SVG

            has_ipython = True
        except ImportError:
            has_ipython = False

        dot_str = self._build_basis_graph().to_dot(
            lambda node: {"label": node["label"]}, lambda edge: edge
        )
        dot = pydot.graph_from_dot_data(dot_str)[0]
        if filename:
            extension = filename.split(".")[-1]
            dot.write(filename, format=extension)
            return None

        if has_ipython:
            svg = dot.create_svg(prog="dot")
            return SVG(svg)

        png = dot.create_png(prog="dot")
        return Image.open(io.BytesIO(png))

    def _build_basis_graph(self):
        graph = rx.PyDiGraph()

        node_map = {}
        for key in self._get_all_keys():
            name, num_qubits = key
            equivalences = self._get_equivalences(key)

            basis = frozenset([f"{name}/{num_qubits}"])
            for params, decomp in equivalences:
                decomp_basis = frozenset(
                    f"{name}/{num_qubits}"
                    for name, num_qubits in {
                        (inst.name, inst.num_qubits) for inst, _, __ in decomp.data
                    }
                )
                if basis not in node_map:
                    basis_node = graph.add_node({"basis": basis, "label": str(set(basis))})
                    node_map[basis] = basis_node
                if decomp_basis not in node_map:
                    decomp_basis_node = graph.add_node(
                        {"basis": decomp_basis, "label": str(set(decomp_basis))}
                    )
                    node_map[decomp_basis] = decomp_basis_node

                label = "{}\n{}".format(str(params), str(decomp) if num_qubits <= 5 else "...")
                graph.add_edge(
                    node_map[basis],
                    node_map[decomp_basis],
                    dict(label=label, fontname="Courier", fontsize=str(8)),
                )

        return graph

    def _get_all_keys(self):
        base_keys = self._base._get_all_keys() if self._base is not None else set()

        self_keys = set(self._map.keys())

        return self_keys | {
            base_key
            for base_key in base_keys
            if base_key not in self._map or self._map[base_key].search_base
        }

    def _get_equivalences(self, key):
        search_base, equivalences = self._map.get(key, (True, []))

        if search_base and self._base is not None:
            return equivalences + self._base._get_equivalences(key)
        return equivalences


def _raise_if_param_mismatch(gate_params, circuit_parameters):
    gate_parameters = [p for p in gate_params if isinstance(p, ParameterExpression)]

    if set(gate_parameters) != circuit_parameters:
        raise CircuitError(
            "Cannot add equivalence between circuit and gate "
            "of different parameters. Gate params: {}. "
            "Circuit params: {}.".format(gate_parameters, circuit_parameters)
        )


def _raise_if_shape_mismatch(gate, circuit):
    if gate.num_qubits != circuit.num_qubits or gate.num_clbits != circuit.num_clbits:
        raise CircuitError(
            "Cannot add equivalence between circuit and gate "
            "of different shapes. Gate: {} qubits and {} clbits. "
            "Circuit: {} qubits and {} clbits.".format(
                gate.num_qubits, gate.num_clbits, circuit.num_qubits, circuit.num_clbits
            )
        )


def _rebind_equiv(equiv, query_params):
    equiv_params, equiv_circuit = equiv
    param_map = dict(zip(equiv_params, query_params))
    equiv = equiv_circuit.assign_parameters(param_map, inplace=False)

    return equiv