def linear_function(a):
    """
    Defines a typical linear encoding / decoding function, essentially a
    pass-through function.

    Parameters
    ----------
    a : numeric or array_like
        Array to encode / decode.

    Returns
    -------
    numeric or ndarray
        Encoded / decoded array.

    Examples
    --------
    >>> linear_function(0.18)
    0.18
    """
    return a
