Performs a Laplace approximation to the posterior

        Parameters
        ----------
        obj_type : method
            Whether a likelihood or a posterior

        Returns
        ----------
        None (plots posterior)

def _laplace_fit(self,obj_type):
        """ Performs a Laplace approximation to the posterior

        Parameters
        ----------
        obj_type : method
            Whether a likelihood or a posterior

        Returns
        ----------
        None (plots posterior)
        """

        # Get Mode and Inverse Hessian information
        y = self.fit(method='PML',printer=False)

        if y.ihessian is None:
            raise Exception("No Hessian information - Laplace approximation cannot be performed")
        else:

            self.latent_variables.estimation_method = 'Laplace'

            theta, Y, scores, states, states_var, X_names = self._categorize_model_output(self.latent_variables.get_z_values())

            # Change this in future
            try:
                latent_variables_store = self.latent_variables.copy()
            except:
                latent_variables_store = self.latent_variables

            return LaplaceResults(data_name=self.data_name,X_names=X_names,model_name=self.model_name,
                model_type=self.model_type, latent_variables=latent_variables_store,data=Y,index=self.index,
                multivariate_model=self.multivariate_model,objective_object=obj_type, 
                method='Laplace',ihessian=y.ihessian,signal=theta,scores=scores,
                z_hide=self._z_hide,max_lag=self.max_lag,states=states,states_var=states_var)