We consider the problem of information flow over Gaussian relay networks.
Similar to the recent work by Avestimehr \emph{et al.} [1], we propose network
codes that achieve up to a constant gap from the capacity of such networks.
However, our proposed codes are also computationally tractable. Our main
technique is to use the codes of Avestimehr \emph{et al.} as inner codes in a
concatenated coding scheme.