@unpublished{ Li:2017, author = {Guanglian Li}, title = {Low-Rank Approximation to Heterogeneous Elliptic Problems}, year = {2017}, note = {INS preprint No. 1704.}, personid = {341}, inspreprintnum= {1704}, pdf = {http://wissrech.ins.uni-bonn.de/research/pub/li/INSPreprint1704.pdf} }