'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(MarkovAutoregression, self).untransform_params(constrained)
    for i in range(self.k_regimes):
        s = self.parameters[(i, 'autoregressive')]
        unconstrained[s] = unconstrain_stationary_univariate(constrained[s])
    return unconstrained
