def METHOD_NAME(n, z, derivative=False):
    r"""Modified spherical Bessel function of the first kind or its derivative.
    Defined as [1]_,
    .. math:: i_n(z) = \sqrt{\frac{\pi}{2z}} I_{n + 1/2}(z),
    where :math:`I_n` is the modified Bessel function of the first kind.
    Parameters
    ----------
    n : int, array_like
        Order of the Bessel function (n >= 0).
    z : complex or float, array_like
        Argument of the Bessel function.
    derivative : bool, optional
        If True, the value of the derivative (rather than the function
        itself) is returned.
    Returns
    -------
    in : ndarray
    Notes
    -----
    The function is computed using its definitional relation to the
    modified cylindrical Bessel function of the first kind.
    The derivative is computed using the relations [2]_,
    .. math::
        i_n' = i_{n-1} - \frac{n + 1}{z} i_n.
        i_1' = i_0
    .. versionadded:: 0.18.0
    References
    ----------
    .. [1] https://dlmf.nist.gov/10.47.E7
    .. [2] https://dlmf.nist.gov/10.51.E5
    """
    if derivative:
        return _spherical_in_d(n, z)
    else:
        return _spherical_in(n, z)