New lower bounds for asymmetric and unidirectional codes

We present new lower bounds on the sizes of asymmetric codes and unidirectional codes. We use various methods, three of them are of special interest. The first is the parti­ tioning method which is a generalization of a method used to construct constant weight codes. The second is combining codes method which is used to obtain a new code from a few others. The third method is shortening by weights which is applied on symmetric codes or on codes generated by the combining codes method. We present a table for the sizes of codes of length nS23. • The author is with the Computer Science Department, Technion, Haifa 3200<l. Israel. The research was supported in part by Technion V.P.R. Fund Albert Einstein Research Fund. This work was presented at the IEEE International Symposium on Information Theory, San Diego, 1990. T ec hn io n C om pu te r Sc ie nc e D ep ar tm en t T eh ni ca l R ep or t C S0 61 8 19 90