-
    z : array_like
        Points at which to evaluate Spence's function
    out : ndarray, optional
        Optional output array for the function results

    Returns
    -------
    s : scalar or ndarray
        Computed values of Spence's function

    Notes
    -----
    There is a different convention which defines Spence's function by
    the integral

    .. math::
      -\int_0^z \frac{\log(1 - t)}{t}dt;

    this is our ``spence(1 - z)``.

    Examples
    --------
    >>> import numpy as np
    >>> from scipy.special import spence
    >>> import matplotlib.pyplot as plt

    The function is defined for complex inputs:

    >>> spence([1-1j, 1.5+2j, 3j, -10-5j])
    array([-0.20561676+0.91596559j, -0.86766909-1.39560134j,
           -0.59422064-2.49129918j, -1.14044398+6.80075924j])

    For complex inputs on the branch cut, which is the negative real axis,
    the function returns the limit for ``z`` with positive imaginary part.
    For example, in the following, note the sign change of the imaginary
    part of the output for ``z = -2`` and ``z = -2 - 1e-8j``:

    >>> spence([-2 + 1e-8j, -2, -2 - 1e-8j])
    array([2.32018041-3.45139229j, 2.32018042-3.4513923j ,
           2.32018041+3.45139229j])

    The function returns ``nan`` for real inputs on the branch cut:

    >>> spence(-1.5)
    nan

    Verify some particular values: ``spence(0) = pi**2/6``,
    ``spence(1) = 0`` and ``spence(2) = -pi**2/12``.

    >>> spence([0, 1, 2])
    array([ 1.64493407,  0.        , -0.82246703])
    >>> np.pi**2/6, -np.pi**2/12
    (1.6449340668482264, -0.8224670334241132)

    Verify the identity::

        spence(z) + spence(1 - z) = pi**2/6 - log(z)*log(1 - z)

    >>> z = 3 + 4j
    >>> spence(z) + spence(1 - z)
    (-2.6523186143876067+1.8853470951513935j)
    >>> np.pi**2/6 - np.log(z)*np.log(1 - z)
    (-2.652318614387606+1.885347095151394j)

    Plot the function for positive real input.

    >>> fig, ax = plt.subplots()
    >>> x = np.linspace(0, 6, 400)
    >>> ax.plot(x, spence(x))
    >>> ax.grid()
    >>> ax.set_xlabel('x')
    >>> ax.set_title('spence(x)')
    >>> plt.show()
    Ú