Three New Methods For Construction Of Extremal Type II Z4-Codes

Three new methods for construction of extremal Type II Z4-codes are discussed. The first method, the doubling method, is developed by the author. The other two methods are generalizations of the building-up method and another construction method developed by Masaaki Harada. Type II codes of length 32 and 40 are discussed. A total of 779 and 1065 extremal Type II codes of length 32 and 40 are found with the three methods. All three methods can help find new extremal Type II codes with a known Type II code. The three methods can be applied on other lengths as well.