Gildea, JoeKaya, AbidinYildiz, Bahattin2019-07-292019-07-292019-08-07Gildea, J., Kaya, A. & Yildiz, B. (2019). An Altered Four Circulant Construction for Self-Dual Codes from Group Rings and New Extremal Binary Self-dual Codes I. Discrete Mathematics, 342(12), 1116200012-365X10.1016/j.disc.2019.111620http://hdl.handle.net/10034/622439We introduce an altered version of the four circulant construction over group rings for self-dual codes. We consider this construction over the binary field, the rings F2 + uF2 and F4 + uF4; using groups of order 4 and 8. Through these constructions and their extensions, we find binary self-dual codes of lengths 16, 32, 48, 64 and 68, many of which are extremal. In particular, we find forty new extremal binary self-dual codes of length 68, including twelve new codes with \gamma=5 in W68,2, which is the first instance of such a value in the literature.enhttp://creativecommons.org/licenses/by-nc-nd/4.0/Group ringsself-dual codescodes over ringsextremal codesfour circulant constructionsArticle1872-681XDiscrete Mathematics