1.
Domain adaptation addresses the problem of generalizing from asourcedistribution for which we have ample labeled training data to atargetdistribution
for which we have little or no labels
Domain adaptation algorithms that do not use labeled target domain data are sometimes calledunsupervisedadaptation algorithms
Domain adaption tends to transfer knowledge across domains following dissimilar distribution and where target domain has inadequate labelled samples.
2.
Traditional machine learning algorithms work well under an assumption that training data in source domain and test data in target domain follow the same distribution. However, the real-world data may not follow this assumption due to the mismatch between training and test conditions.
are deployed in practise, the conditions in which test data is acquired do not exactly match those of the training set.
4. pseudo label
Most of the previous deep domain adaptation methods have been proposed mainly under the assumption that the adaptation can be realized by matching the distribution of features from different
domains. These methods aimed to obtain domain-invariant features by minimizing the divergence between domains as well as a category loss on
the source domain (Ganin & Lempitsky,
2014;
Long et al.,
2015b;
2016). However, as shown in (Ben-David
et al.,
2010), theoretically, if a classifier that works well on both
the source and the target domains does not exist, we cannot expect a discriminative classifier for the target domain. That is, even if the distributions are matched on the nondiscriminative representations, the classifier may not work
well on the target domain. Since directly learning discriminative representations for the target domain, in the absence of target labels, is considered very difficult, we propose to assign
pseudo-labels to target samples and train targetspecific networks as if they were true labels
5.
Pan and Yang [22] presented taxonomy
of TL methods which include Inductive TL, when labelled samples are available in both source and target domains; Transductive TL, when labels are only available in the source set, and Unsupervised TL, when labelled data is not present。