'Gaussian deviance residuals
Parameters
endog : array-like
Endogenous response variable
mu : array-like
Fitted mean response variable
scale : float, optional
An optional argument to divide the residuals by scale. The default
is 1.
Returns
resid_dev : array
Deviance residuals as defined below
Notes
.. math::
resid\_dev_i = (Y_i - \mu_i) / \sqrt{scale}'

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

    return ((endog - mu) / (scale ** 0.5))
