Components of a probabilistic machine learning classifier: Like naive Bayes, logistic regression is a probabilistic classifier that makes use of supervised machine learning. Machine learning classifiers require a training corpus of m input/output pairs (x (i) , y (i) ). (We'll use superscripts in parentheses to refer to individual instances in the training set-for sentiment classification each instance might be an individual document to be classified). A machine learning system for classification then has four components: