Bao-Xing Chen Wenjun Xiao Optimal Designs of Directed Double-Loop Networks. 19-24 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3314&spage=19 2004 conf/cis/2004 CIS db/conf/cis/cis2004.html#ChenX04