  This paper uses information-theoretic tools to analyze the generalization
error in unsupervised domain adaptation (UDA). We present novel upper bounds
for two notions of generalization errors. The first notion measures the gap
between the population risk in the target domain and that in the source domain,
and the second measures the gap between the population risk in the target
domain and the empirical risk in the source domain. While our bounds for the
first kind of error are in line with the traditional analysis and give similar
insights, our bounds on the second kind of error are algorithm-dependent, which
also provide insights into algorithm designs. Specifically, we present two
simple techniques for improving generalization in UDA and validate them
experimentally.
