Resumen
Building-up construction is one of several methods for constructing self-dual codes. Recently, a new building-up construction method has been developed by S. Han, in which the existence of a square matrix U such that ??????=-??
U
U
T
=
-
I
is essential. In this paper, we completely solve the existence problem for U over Z????
Z
p
m
, where p is an arbitrary prime number.