An overview of covariance operators in Hilbert space, and their applications
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If you have a question about this talk, please contact Karsten Borgwardt.
Many problems in unsupervised learning require the analysis
of features of probability distributions. In this talk, we deal with
the problem of measuring dependence between random variables, using
the covariance between maps of these variables to spaces of
features. When the feature spaces are universal reproducing kernel
Hilbert spaces (RKHSs), it can be shown that the covariance is zero
only when the variables are independent.
A different perspective on these operators arises when one seeks to
manipulate variables so as to maximise their dependence (as measured
by feature space covariance), rather than minimising it. In the case
of feature selection, we would choose those features that maximise the
dependence with respect to particular target variables. Several
well-known feature selection algorithms can be recovered through an
appropriate feature space choice. Finally, covariance operators may
be combined to give measures of conditional covariance, which may be
used to measure conditional dependence.
This talk is part of the Machine Learning @ CUED series.
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