def METHOD_NAME(self, x):
    def f1(xx):
        x2m1 = xx * xx - 1
        sqx2m1 = np.sqrt(-x2m1)
        return (-3 / 2 / x2m1**2
                + (x2m1+3) * np.arcsinh(sqx2m1 / xx) / 2 / (-x2m1)**2.5)
    def f2(xx):
        x2m1 = xx * xx - 1
        sqx2m1 = np.sqrt(x2m1)
        return (-3 / 2 / x2m1**2
                + (x2m1+3) * np.arcsin(sqx2m1 / xx) / 2 / x2m1**2.5)
    xf = x.flatten()
    return np.piecewise(xf,
                        [xf < 1, xf > 1],
                        [f1, f2, 2./15.]).reshape(x.shape)