'Return predicted values from a design matrix.
Parameters
params : array-like
Parameters of a mixed linear model.  Can be either a
MixedLMParams instance, or a vector containing the packed
model parameters in which the fixed effects parameters are
at the beginning of the vector, or a vector containing
only the fixed effects parameters.
exog : array-like, optional
Design / exogenous data for the fixed effects. Model exog
is used if None.
Returns
An array of fitted values.  Note that these predicted values
only reflect the fixed effects mean structure of the model.'

def predict(self, params, exog=None):

    if (exog is None):
        exog = self.exog
    if isinstance(params, MixedLMParams):
        params = params.fe_params
    else:
        params = params[0:self.k_fe]
    return np.dot(exog, params)
