:param link_f: latent variables (link(f))
        :type link_f: Nx1 array
        :param y: data
        :type y: Nx1 array
        :param Y_metadata: includes censoring information in dictionary key 'censored'
        :returns: likelihood evaluated for this point
        :rtype: float

def logpdf_link(self, link_f, y, Y_metadata=None):
        """
        :param link_f: latent variables (link(f))
        :type link_f: Nx1 array
        :param y: data
        :type y: Nx1 array
        :param Y_metadata: includes censoring information in dictionary key 'censored'
        :returns: likelihood evaluated for this point
        :rtype: float
        """
        assert np.atleast_1d(link_f).shape == np.atleast_1d(y).shape
        c = np.zeros_like(y)
        if Y_metadata is not None and 'censored' in Y_metadata.keys():
            c = Y_metadata['censored']

        uncensored = (1-c)* (-0.5*np.log(2*np.pi*self.variance) - np.log(y) - (np.log(y)-link_f)**2 /(2*self.variance) )
        censored = c*np.log( 1 - stats.norm.cdf((np.log(y) - link_f)/np.sqrt(self.variance)) )
        logpdf = uncensored + censored
        return logpdf