In this correspondence, we give two computational results on binary self-dual codes. A number of extremal singly-even self-dual [68, 34, 12] codes with weight enumerators not known to exist, are constructed. For k < 10, the relationship between extremal doubly-even self-dual codes of length 24fc, and certain singly-even self-dual codes of length 24k -2 is presented.
- New extremal doubly-even codes
- Shadow codes
- Weight enumerators