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Domain Adaptation is a field associated with machine learning and transfer learning. This scenario arises when we aim at learning from a source data distribution a well performing model on a different (but related) target data distribution. For instance, one of the tasks of the common spam filtering problem consists in adapting a model from one user (the source distribution) to a new one who receives significantly different emails (the target distribution). Note that, when more than one source distribution is available we talked about multi-source domain adaptation. == Formalization == Let be the input space (or description space) and let be the output space (or label space). The objective of a machine learning algorithm is to learn a mathematical model (a hypothesis) able to affect a label of to an example from . This model is learned from a learning sample . Usually in supervised learning (without domain adaptation), we suppose that the examples are drawn i.i.d. from a distribution of support (unknown and fixed). The objective is then to learn (from ) such that it commits the least error as possible for labelling new examples coming from the distribution . The main difference between supervised learning and domain adaptation is that in the latter situation we study two different (but related) distributions and on . The domain adaptation task then consists of the transfer of knowledge from the source domain to the target one . The goal is then to learn (from labeled or unlabelled samples coming from the two domains) such that it commits as little error as possible on the target domain . The major issue is the following: if a model is learned from a source domain, what is its capacity to correctly label data coming from the target domain? == The different types of domain adaptation == There are several contexts of domain adaptation. They differ in the informations considered for the target task. # The unsupervised domain adaptation: the learning sample contains a set of labeled source examples, a set of unlabeled source examples and an unlabeled set of target examples. # The semi-supervised domain adaptation: in this situation, we also consider a "small" set of labeled target examples. # The supervised domain adaptation: all the examples considered are supposed to be labeled. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Domain adaptation」の詳細全文を読む スポンサード リンク
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