Targeting at sparse learning, we construct Banach spaces B of functions on an
input space X with the properties that (1) B possesses an l1 norm in the sense
that it is isometrically isomorphic to the Banach space of integrable functions
on X with respect to the counting measure; (2) point evaluations are continuous
linear functionals on B and are representable through a bilinear form with a
kernel function; (3) regularized learning schemes on B satisfy the linear
representer theorem. Examples of kernel functions admissible for the
construction of such spaces are given.

本文针对稀疏学习，构建函数 Banach 空间 B，该空间对于输入空间 X 中的可积函数采用计数测度下的 l1 范数与 B 等距同构；同时，点评价运算是 B 上的连续线性泛函，并且可表示为具有核函数的双线性形式；最后，本文证明了在 B 上正则化学习方案适用于线性表述定理。同时，本文还提供了构建这些空间的核函数实例。

带 l1 范数的再生核 Banach 空间

Reproducing Kernel Banach Spaces with the l1 Norm

This paper is about a curious phenomenon. Suppose we have a data matrix,
which is the superposition of a low-rank component and a sparse component. Can
we recover each component individually? We prove that under some suitable
assumptions, it is possible to recover both the low-rank and the sparse
components exactly by solving a very convenient convex program called Principal
Component Pursuit; among all feasible decompositions, simply minimize a
weighted combination of the nuclear norm and of the L1 norm. This suggests the
possibility of a principled approach to robust principal component analysis
since our methodology and results assert that one can recover the principal
components of a data matrix even though a positive fraction of its entries are
arbitrarily corrupted. This extends to the situation where a fraction of the
entries are missing as well. We discuss an algorithm for solving this
optimization problem, and present applications in the area of video
surveillance, where our methodology allows for the detection of objects in a
cluttered background, and in the area of face recognition, where it offers a
principled way of removing shadows and specularities in images of faces.

本文介绍了一种名为主成分追踪的凸型优化方法，能在有噪声或缺损情况下准确分离一个 $ m * n $ 数据矩阵的低秩和稀疏成分，该方法有望应用于视频监控和人脸识别等领域。