Increased classification accuracy and speedup through pair-wise feature selection for support vector machines

Support vector machines are binary classifiers that can implement multi-class classifiers by creating a classifier for each possible combination of classes or for each class using a one class versus all strategy. Feature selection algorithms often search for a single set of features to be used by each of the binary classifiers. This ignores the fact that features that may be good discriminators for two particular classes might not do well for other class combinations. As a result, the feature selection process may not include these features in the common set to be used by all support vector machines. It is shown that by selecting features for each binary class combination, overall classification accuracy can be improved (as much as 2.1%), feature selection time can be significantly reduced (speed up of 3.2 times), and time required for training a multi-class support vector machine is reduced. Another benefit of this approach is that considerably less time is required for feature selection when additional classes are added to the training data. This is because the features selected for the existing class combinations are still valid, so that feature selection only needs to be run for the new class combinations created.