'Transform constrained parameters used in likelihood evaluation
to unconstrained parameters used by the optimizer
Parameters
constrained : array_like
Array of constrained parameters used in likelihood evalution, to be
transformed.
Returns
unconstrained : array_like
Array of unconstrained parameters used by the optimizer.'

def untransform_params(self, constrained):

    unconstrained = super(MarkovRegression, self).untransform_params(constrained)
    unconstrained[self.parameters['exog']] = constrained[self.parameters['exog']]
    unconstrained[self.parameters['variance']] = (constrained[self.parameters['variance']] ** 0.5)
    return unconstrained
