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Relevance vector machine

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In mathematics, a Relevance Vector Machine (RVM) is a machine learning technique that uses Bayesian inference to obtain parsimonious solutions for regression and probabilistic classification.[1] A greedy optimisation procedure and thus fast version were subsequently developed.[2] [3] The RVM has an identical functional form to the support vector machine, but provides probabilistic classification.

It is actually equivalent to a Gaussian process model with covariance function:

k ( x , x ) = j = 1 N 1 α j φ ( x , x j ) φ ( x , x j ) {\displaystyle k(\mathbf {x} ,\mathbf {x'} )=\sum _{j=1}^{N}{\frac {1}{\alpha _{j}}}\varphi (\mathbf {x} ,\mathbf {x} _{j})\varphi (\mathbf {x} ',\mathbf {x} _{j})} {\displaystyle k(\mathbf {x} ,\mathbf {x'} )=\sum _{j=1}^{N}{\frac {1}{\alpha _{j}}}\varphi (\mathbf {x} ,\mathbf {x} _{j})\varphi (\mathbf {x} ',\mathbf {x} _{j})}

where φ {\displaystyle \varphi } {\displaystyle \varphi } is the kernel function (usually Gaussian), α j {\displaystyle \alpha _{j}} {\displaystyle \alpha _{j}} are the variances of the prior on the weight vector w N ( 0 , α 1 I ) {\displaystyle w\sim N(0,\alpha ^{-1}I)} {\displaystyle w\sim N(0,\alpha ^{-1}I)}, and x 1 , , x N {\displaystyle \mathbf {x} _{1},\ldots ,\mathbf {x} _{N}} {\displaystyle \mathbf {x} _{1},\ldots ,\mathbf {x} _{N}} are the input vectors of the training set.[4]

Compared to that of support vector machines (SVM), the Bayesian formulation of the RVM avoids the set of free parameters of the SVM (that usually require cross-validation-based post-optimizations). However RVMs use an expectation maximization (EM)-like learning method and are therefore at risk of local minima. This is unlike the standard sequential minimal optimization (SMO)-based algorithms employed by SVMs, which are guaranteed to find a global optimum (of the convex problem).

The relevance vector machine was patented in the United States by Microsoft (patent expired September 4, 2019).[5]

See also

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References

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  1. ^ Tipping, Michael E. (2001). "Sparse Bayesian Learning and the Relevance Vector Machine". Journal of Machine Learning Research . 1: 211–244.
  2. ^ Tipping, Michael; Faul, Anita (2003). "Fast Marginal Likelihood Maximisation for Sparse Bayesian Models". Proceedings of the Ninth International Workshop on Artificial Intelligence and Statistics: 276–283. Retrieved 21 November 2024.
  3. ^ Faul, Anita; Tipping, Michael (2001). "Analysis of Sparse Bayesian Learning" (PDF). Advances in Neural Information Processing Systems. Retrieved 21 November 2024.
  4. ^ Candela, Joaquin Quiñonero (2004). "Sparse Probabilistic Linear Models and the RVM". Learning with Uncertainty - Gaussian Processes and Relevance Vector Machines (PDF) (Ph.D.). Technical University of Denmark. Retrieved April 22, 2016.
  5. ^ US 6633857, Michael E. Tipping, "Relevance vector machine" 

Software

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