Refinement of operator-valued reproducing kernels

  • Authors:
  • Haizhang Zhang;Yuesheng Xu;Qinghui Zhang

  • Affiliations:
  • School of Mathematics and Computational Science, Sun Yat-sen University, Guangzhou, P. R. China and Guangdong Province Key Laboratory of Computational Science;Department of Mathematics, Syracuse University, Syracuse, NY and Guangdong Province Key Laboratory of Computational Science, Sun Yat-sen University, Guangzhou, P. R. China;School of Mathematics and Computational Science, Sun Yat-sen University, Guangzhou, P. R. China

  • Venue:
  • The Journal of Machine Learning Research
  • Year:
  • 2012

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Abstract

This paper studies the construction of a refinement kernel for a given operator-valued reproducing kernel such that the vector-valued reproducing kernel Hilbert space of the refinement kernel contains that of the given kernel as a subspace. The study is motivated from the need of updating the current operator-valued reproducing kernel in multi-task learning when underfitting or overfitting occurs. Numerical simulations confirm that the established refinement kernel method is able to meet this need. Various characterizations are provided based on feature maps and vector-valued integral representations of operator-valued reproducing kernels. Concrete examples of refining translation invariant and finite Hilbert-Schmidt operator-valued reproducing kernels are provided. Other examples include refinement of Hessian of scalar-valued translation-invariant kernels and transformation kernels. Existence and properties of operator-valued reproducing kernels preserved during the refinement process are also investigated.