def METHOD_NAME(self,uh,indx,cfun = None):
    ws = self.qf.weights
    bcs = self.qf.quadpts
    pp = self.space.bc_to_point_cell(bcs)
    gu = self.pde.gradient(pp)
    error1 = self.get_DG_error(uh,cfun)
    if cfun is not None:
        a = self.pde.diffusion_coefficient(pp)
        a_K = np.einsum('t, tm->m', ws, a)
        error2 = np.einsum('k, kmj,m,m->',ws, gu**2,self.cellmeasure,a_K)
    else:
        error2 = np.einsum('k, kmj,m->',ws, gu**2,self.cellmeasure)
    error = error1/sqrt(error2)
    return error