Source code for psipose.encoders._base

"""Base encoder class."""

import abc

import pennylane as qml




class BaseEncoder(abc.ABC):
    """Abstract base class for quantum encoders.

    Encoders map classical feature vectors onto quantum states.

    Parameters
    ----------
    n_qubits : int, optional
        Number of qubits to encode into. If None, inferred from feature dimension.

    Attributes
    ----------
    n_qubits_ : int
        The number of qubits used (determined during fit).
    """

    def __init__(self, n_qubits=None):
        self.n_qubits = n_qubits
        self.n_qubits_ = None



    @abc.abstractmethod
    def encode(self, x, wires):
        """Apply encoding circuit to the given wires.

        Parameters
        ----------
        x : array-like
            Feature vector to encode.
        wires : Iterable[int]
            Qubit wires to apply the encoding to.
        """
        pass




    def fit(self, X):
        """Determine the number of qubits needed based on data.

        Parameters
        ----------
        X : array-like, shape (n_samples, n_features)
            Training data.

        Returns
        -------
        self : BaseEncoder
            Returns the fitted encoder.
        """
        n_features = X.shape[1]
        if self.n_qubits is None:
            # Default: one qubit per feature, capped at reasonable size
            self.n_qubits_ = min(n_features, 10)
        else:
            self.n_qubits_ = self.n_qubits
        return self




    def transform(self, X):
        """Encode the data into quantum states.

        Parameters
        ----------
        X : array-like, shape (n_samples, n_features)
            Data to encode.

        Returns
        -------
        quantum_states : list
            List of quantum state descriptions (implementation-specific).
        """
        states = []
        for x in X:
            with qml.tape.QuantumTape() as tape:
                self.encode(x, wires=range(self.n_qubits_))
            states.append(tape)
        return states