在机器学习中,表征学习或表示学习是允许系统从原始数据中自动发现特征检测或分类所需的表示的一组技术。这取代了手动特征工程,并允许机器学习特征并使用它们执行特定任务。在有监督的表征学习中,使用标记的输入数据来学习特征,包括监督神经网络,多层感知器和(监督)字典学习。在无监督表征学习中,特征是与未标记的输入数据一起学习的,包括字典学习,独立成分分析,自动编码器,矩阵分解和各种形式的聚类。

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我们生活在一个由大量不同模态内容构建而成的多媒体世界中,不同模态信息之间具有高度的相关性和互补性,多模态表征学习的主要目的就是挖掘出不同模态之间的共性和特性,产生出可以表示多模态信息的隐含向量.该文章主要介绍了目前应用较广的视觉语言表征的相应研究工作,包括传统的基于相似性模型的研究方法和目前主流的基于语言模型的预训练的方法.目前比较好的思路和解决方案是将视觉特征语义化然后与文本特征通过一个强大的特征抽取器产生出表征,其中Transformer[1]作为主要的特征抽取器被应用表征学习的各类任务中.文章分别从研究背景、不同研究方法的划分、测评方法、未来发展趋势等几个不同角度进行阐述.

http://www.jos.org.cn/jos/ch/reader/view_abstract.aspx?file_no=6125&flag=1

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It has been recently shown that general policies for many classical planning domains can be expressed and learned in terms of a pool of features defined from the domain predicates using a description logic grammar. At the same time, most description logics correspond to a fragment of $k$-variable counting logic ($C_k$) for $k=2$, that has been shown to provide a tight characterization of the expressive power of graph neural networks. In this work, we make use of these results to understand the power and limits of using graph neural networks (GNNs) for learning optimal general policies over a number of tractable planning domains where such policies are known to exist. For this, we train a simple GNN in a supervised manner to approximate the optimal value function $V^{*}(s)$ of a number of sample states $s$. As predicted by the theory, it is observed that general optimal policies are obtained in domains where general optimal value functions can be defined with $C_2$ features but not in those requiring more expressive $C_3$ features. In addition, it is observed that the features learned are in close correspondence with the features needed to express $V^{*}$ in closed form. The theory and the analysis of the domains let us understand the features that are actually learned as well as those that cannot be learned in this way, and let us move in a principled manner from a combinatorial optimization approach to learning general policies to a potentially, more robust and scalable approach based on deep learning.

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It has been recently shown that general policies for many classical planning domains can be expressed and learned in terms of a pool of features defined from the domain predicates using a description logic grammar. At the same time, most description logics correspond to a fragment of $k$-variable counting logic ($C_k$) for $k=2$, that has been shown to provide a tight characterization of the expressive power of graph neural networks. In this work, we make use of these results to understand the power and limits of using graph neural networks (GNNs) for learning optimal general policies over a number of tractable planning domains where such policies are known to exist. For this, we train a simple GNN in a supervised manner to approximate the optimal value function $V^{*}(s)$ of a number of sample states $s$. As predicted by the theory, it is observed that general optimal policies are obtained in domains where general optimal value functions can be defined with $C_2$ features but not in those requiring more expressive $C_3$ features. In addition, it is observed that the features learned are in close correspondence with the features needed to express $V^{*}$ in closed form. The theory and the analysis of the domains let us understand the features that are actually learned as well as those that cannot be learned in this way, and let us move in a principled manner from a combinatorial optimization approach to learning general policies to a potentially, more robust and scalable approach based on deep learning.

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