Optimal double circulant self-dual codes over F4

Optimal double circulant self-dual codes over F-4 have been found for each length n less than or equal to 40. For lengths n less than or equal to 14, 20, 22, 24, 28, and 30, these codes are optimal self-dual codes. For length 26, the code attains the highest known minimum weight. For n greater than or equal to 32, the codes presented provide the highest known minimum weights. The [36, 18, 12] self-dual code improves the lower bound on the highest minimum weight for a [36, 18] linear code.