def getLaplaceCovar(self):
        """
        USES LAPLACE APPROXIMATION TO CALCULATE THE COVARIANCE MATRIX OF THE OPTIMIZED PARAMETERS
        """
        assert self.init,        'GP not initialised'
        assert self.fast==False, 'Not supported for fast implementation'
        
        if self.cache['Sigma']==None:
            self.cache['Sigma'] = SP.linalg.inv(self.getHessian())
        return self.cache['Sigma']