In the list of optimal regular graph designs (RGDs) provided by J. A. John and Mitchell, the E-optimality of some designs is still unknown. We have found the answers for some parameter sets including type of $(v,~v,~2),~(v,~v,~v-2)$. These E-optimal regular graph designs added by BIBDs are again E-optimal under certain domain.
Taiwanese J. Math.
1(1):
47-57
(1997).
DOI: 10.11650/twjm/1500404924
