--------
    Basic homogeneity property:

    >>> import numpy as np
    >>> from scipy.special import elliprd

    >>> x = 1.2 + 3.4j
    >>> y = 5.
    >>> z = 6.
    >>> scale = 0.3 + 0.4j
    >>> elliprd(scale*x, scale*y, scale*z)
    (-0.03703043835680379-0.24500934665683802j)

    >>> elliprd(x, y, z)*np.power(scale, -1.5)
    (-0.0370304383568038-0.24500934665683805j)

    All three arguments coincide:

    >>> x = 1.2 + 3.4j
    >>> elliprd(x, x, x)
    (-0.03986825876151896-0.14051741840449586j)

    >>> np.power(x, -1.5)
    (-0.03986825876151894-0.14051741840449583j)

    The so-called "second lemniscate constant":

    >>> elliprd(0, 2, 1)/3
    0.5990701173677961

    >>> from scipy.special import gamma
    >>> gamma(0.75)**2/np.sqrt(2*np.pi)
    0.5990701173677959

    Ú