Machine Learning (Theory)

2/9/2005

Intuitions from applied learning

Tags: General jl@ 7:54 pm

Since learning is far from an exact science, it’s good to pay attention to basic intuitions of applied learning. Here are a few I’ve collected.

  1. Integration In Bayesian learning, the posterior is computed by an integral, and the optimal thing to do is to predict according to this integral. This phenomena seems to be far more general. Bagging, Boosting, SVMs, and Neural Networks all take advantage of this idea to some extent. The phenomena is more general: you can average over many different classification predictors to improve performance. Sources: Zoubin, Caruana
  2. Differentiation Different pieces of an average should differentiate to achieve good performance by different methods. This is know as the ‘symmetry breaking’ problem for neural networks, and it’s why weights are initialized randomly. Boosting explicitly attempts to achieve good differentiation by creating new, different, learning problems. Sources: Yann LeCun, Phil Long
  3. Deep Representation Having a deep representation is necessary for having a good general learner. Decision Trees and Convolutional neural networks take advantage of this. SVMs get around it by allowing the user to engineer knowledge into the kernel. Boosting and Bagging rely on another algorithm for this. Sources: Yann LeCun
  4. Fine Representation of Bias Many learning theory applications use just a coarse representation of bias such as “function in the hypothesis class or not”. In practice, significantly better performance is achieved from a more finely tuned bias. Bayesian learning has this builtin with a prior. Other techniques can take advantage of this as well. Sources: Zoubin, personal experience.

If you have others, please comment on them.

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