%0 Journal Article
%T Some results on communicating the sum of sources over a network
%A Brijesh Kumar Rai
%A Bikash Kumar Dey
%A Abhay Karandikar
%J Mathematics
%D 2008
%I arXiv
%X We consider the problem of communicating the sum of $m$ sources to $n$ terminals in a directed acyclic network. Recently, it was shown that for a network of unit capacity links with either $m=2$ or $n=2$, the sum of the sources can be communicated to the terminals if and only if every source-terminal pair is connected in the network. We show in this paper that for any finite set of primes, there exists a network where the sum of the sources can be communicated to the terminals only over finite fields of characteristic belonging to that set. As a corollary, this gives networks where the sum can not be communicated over any finite field even though every source is connected to every terminal.
%U http://arxiv.org/abs/0811.0285v1