Hwanho Kim Jinchao Xu Ludmil Zikatanov Uniformly Convergent Multigrid Methods for Convection-Diffusion Problems without Any Constraint on Coarse Grids. 385-399 2004 20 Adv. Comput. Math. 4 http://dx.doi.org/10.1023/A:1027378015262 db/journals/adcm/adcm20.html#KimXZ04