Vowpal Wabbit (VW) is an open-source fast online interactive machine learning system library and program developed originally at Yahoo!

It was started and is led by John Langford.

Vowpal Wabbit provides an efficient scalable out-of-core implementation with support for a number of machine learning reductions, importance weighting, and a selection of different loss functions and optimization algorithms.

The VW program supports: Vowpal wabbit has been used to learn a tera-feature (1012) data-set on 1000 nodes in one hour.

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