Creates cholesky decomposition of covariance matrix

        Parameters
        ----------
        parm : np.array
            Contains transformed latent variables

        Returns
        ----------
        The cholesky decomposition (L) of K

def _L(self, parm):
        """ Creates cholesky decomposition of covariance matrix

        Parameters
        ----------
        parm : np.array
            Contains transformed latent variables

        Returns
        ----------
        The cholesky decomposition (L) of K
        """ 

        return np.linalg.cholesky(self.kernel.K(parm) + np.identity(self.X().shape[1])*parm[0])