Table 1. Properties of feature representation transfer methods.

	DA type			Properties
Method	Unsup.	Semis.	Sup.	D ≥ 2	Unpaired	dS ≠ dT	Nonlinear
PCA [24]	√				√
KPCA [25]	√				√		√
TCA [10]	√				√		√
SSTCA [10]		√			√		√
JDA [26]		√	$\widehat{y}$		√		√
CCA [22]	√			√		√
kCCA [9]	√			√		√	√
MA [20]			p	√
GM [27]	√				√
OT-lab [15]		√			√		√
SGF [12]	√	√	√		√		√
GFK [13]	√	√	√		√		√
MMDT [18]			√		√
SSMA [23]			√	√	√	√
KEMA			√	√	√	√	√

D: number of domains.

d_S, d_T: number of features in source and target.

$\widehat{y}$: semilabels predicted by a classifier.

p: known corresponding samples, but no labels.