'Estimates the parameters of a VECM.
The estimation procedure is described on pp. 269-304 in [1]_.
Parameters
method : str {"ml"}, default: "ml"
Estimation method to use. "ml" stands for Maximum Likelihood.
Returns
est : :class:`VECMResults`
References
.. [1] Lutkepohl, H. 2005. *New Introduction to Multiple Time Series Analysis*. Springer.'

def fit(self, method='ml'):

    if (method == 'ml'):
        return self._estimate_vecm_ml()
    else:
        raise ValueError(('%s    not    recognized,    must    be    among    %s' % (method, 'ml')))
