'The Anscombe residuals for Gamma distribution
Parameters
endog : array
Endogenous response variable
mu : array
Fitted mean response variable
scale : float, optional
An optional argument to divide the residuals by sqrt(scale).
The default is 1.
Returns
resid_anscombe : array
The Anscombe residuals for the Gamma family defined below
Notes
.. math::
resid\_anscombe_i = 3 * (Y_i^{1/3} - \mu_i^{1/3}) / \mu_i^{1/3}
/ \sqrt{scale}'

def resid_anscombe(self, endog, mu, scale=1.0):

    return (((3 * ((endog ** (1 / 3.0)) - (mu ** (1 / 3.0)))) / (mu ** (1 / 3.0))) / (scale ** 0.5))
