Learning representations on Grassmann manifolds is popular in quite a few
visual recognition tasks. In order to enable deep learning on Grassmann
manifolds, this paper proposes a deep network architecture by generalizing the
Euclidean network paradigm to Grassmann manifolds. In particular, we design
full rank mapping layers to transform input Grassmannian data to more desirable
ones, exploit re-orthonormalization layers to normalize the resulting matrices,
study projection pooling layers to reduce the model complexity in the
Grassmannian context, and devise projection mapping layers to respect
Grassmannian geometry and meanwhile achieve Euclidean forms for regular output
layers. To train the Grassmann networks, we exploit a stochastic gradient
descent setting on manifolds of the connection weights, and study a matrix
generalization of backpropagation to update the structured data. The
evaluations on three visual recognition tasks show that our Grassmann networks
have clear advantages over existing Grassmann learning methods, and achieve
results comparable with state-of-the-art approaches.

本文提出了一种将欧几里得网络范例泛化到 Grassmann 流形的深度网络体系结构，利用完全秩映射层将输入数据转换为更理想的数据，利用再正则化层对结果矩阵进行规范化，利用投影映射层使结构数据进行更新，并在三个视觉识别任务中的评估显示出 Grassmann 网络具有明显优势。

在 Grassmann 流形上构建深度神经网络

Building Deep Networks on Grassmann Manifolds

Recent advances in computer vision and machine learning suggest that a wide
range of problems can be addressed more appropriately by considering
non-Euclidean geometry. In this paper we explore sparse dictionary learning
over the space of linear subspaces, which form Riemannian structures known as
Grassmann manifolds. To this end, we propose to embed Grassmann manifolds into
the space of symmetric matrices by an isometric mapping, which enables us to
devise a closed-form solution for updating a Grassmann dictionary, atom by
atom. Furthermore, to handle non-linearity in data, we propose a kernelised
version of the dictionary learning algorithm. Experiments on several
classification tasks (face recognition, action recognition, dynamic texture
classification) show that the proposed approach achieves considerable
improvements in discrimination accuracy, in comparison to state-of-the-art
methods such as kernelised Affine Hull Method and graph-embedding Grassmann
discriminant analysis.

本文提出了一种在非欧几里得空间上的稀疏字典学习算法，该算法通过将 Grassmann 流形嵌入到对称矩阵空间中来实现。在几种分类任务中，该算法较之目前最先进的方法如核仿射集算法和图嵌入 Grassmann 判别分析具有更好的识别精度。